Bombard is splashable removal that's cheap and removes four toughness creatures, which is a benchmark in the format. The same can basically be said about Luminous Bonds, but it's vulnerable to bounce spells, Disenchants, and isn't an instant. There are also a non-zero number of things you'd prefer to remove outright rather than Luminous Bonds. The argument for ascend is reasonable, but it also keeps a permanent around for your opponent, so it's kind of a wash.
I don't mind moving in on gold cards as early as most players. Your blue decks want splashes and ascend, so Deadeye Brawler shouldn't be seen as a commitment. The real question should be regarding power level, but I like it more than Goblin Trailblazer, Forerunner of the Legion, Evolving Wilds, and Strength of the Pack.
I think Bombard is pretty clearly the best card here. Splashable, instant speed removal that hits the right toughness in this format is a no-brainer. It's not that Luminous Bonds is bad - far from it actually. It's just that Bombard is miles better than it. That said, there are things that Luminous Bonds handles that Bombard doesn't (a giant Dinosaur) or would prefer not to (something with enrage). Then again, there are cards that Bombard cleans up (Vona, Butcher of Magan, any of the Forerunners) that Luminous Bonds technically handles but really doesn't.
Both cards are good. Both cards will make your deck. But one is better than the other.
As for Goblin Trailblazer over Forerunner of the Legion, it's pretty simple honestly. I think that Goblin Trailblazer is one of the best two-drops in the format, and this is a format that's all about two-drops. Some have claimed that this limited format isn't as aggressive as people originally thought, but I haven't found that to be the case yet. Naturally, I love giving beatdowns and I like pairing my hard to block creatures with removal, bounce spells, or pump spells, so Goblin Trailblazer has a home in a lot of my decks. Further, two of my favorite archetypes are U/R Pirates and B/R Pirates, a place where Goblin Trailblazer is at its very best.
There's nothing really wrong with Forerunner of the Legion; it's just not a card I ever get excited about.
I don't actually have a good answer for which of the removal spells is better here, but my general rule is the best splashable removal is better than uncommon tribal payoffs. I also don't buy into the whole "red is bad" nonsense a bunch of people are spreading, though I do think white is pretty solid. The quality level isn't clear cut as Luminous Bonds stops Colossal Dreadmaw because Bombard killing Legion Lieutenant-style threats is important. I'm currently on Bonds, but take whichever one you want.
Immediately after those is Forerunner of the Legion. The uncommon tribal payoffs are all pretty great in this format and let your cards really outclass your opponent's. Forerunner of the Legion is in the top tier of those because it doesn't require a two color commitment. I have had W/U decks where Forerunner was great just because I could get a Sanguine Glorifier or a Skymarch Aspirant, and the +1/+1 matters more than you think. Honestly, the Glorifier three-four setup alone means that if I end up in white Forerunner of the Legion is going to end up in my deck the majority of the time I'm in white even if I'm not dedicated Vampires.
Golden Guardian is kind of a chore to transform, but it gives you some nice inevitability while providing a reasonable blocker early. It's a card you'll almost certainly play, so there's an added bonus, but I don't rate that too highly. If there were a good removal spell or great blue card, I'd be all over those instead.
Siren Reaver and Goblin Trailblazer are both fine. While two-drops are generally more valuable than three-drops (especially because blue has several great threes), Siren Reaver's flying is incredibly important.
Overall, a weak pack.
You ever see a card that has a weird text box, you have to read it a few times to make sure you understand it, and then ask your friends to make sure you're reading it right so that you can evaluate it correctly? That's what I had to do with Golden Guardian. And after all my friends said "It's insane!" I played with it, realized it was insane, and won't ever pass it again. Golden Guardian goes in any deck, is a good cardbefore it transforms, and borders on an unbeatable card after it transforms.
Siren Reaver is a 3/2 flier for three mana. I know it may look like it costs four, but if you draft hyper aggressive decks as much as I do, it costs three. I don't think it's that great or anything, but I'm never cutting it from my deck and flying is pretty dope.
Golden Guardian is messed up. If you haven't had the experience of casting or playing against the card, here is how it goes. First, your opponent looks at a 4/4 and realizes that is actually just too big to beat in this format. Then, you untap and they realize they can never attack on the ground again, as even if Golden Guardian blocks a 2/2 that just lets it fight something and die. Then, eventually you just transform it anyways and they die to 4/4 Golem tokens. It requires no real assistance besides you controlling creatures and is even a colorless first pick.
After that, I take the evasive creatures. Siren Reaver is distinctly better than Goblin Trailblazer. It is actually a three-drop and 3/2 flying is way higher impact than 2/1 menace. I could see an argument for Squire's Devotion as the third card instead of Goblin Trailblazer, but I value two-drops pretty highly and auras still have real downsides even if they are the good ones.
Taking Deeproot Elite and passing Merfolk Mistbinder can be awkward, but if you're doing a good job hard cutting Merfolk, it likely won't matter. Deeproot Elite is incredible, and I wouldn't pass it. It's similar to Merfolk Mistbinder except that it gives you flexibility to go tall if necessary. If it sticks around for a few turns, the damage is often already done, even if they remove it later. Also, you don't need to be full-on Merfolk for Deeproot Elite to make a huge impact.
Everything I said earlier about Bombard applies here. Impale is great, but I'd prefer to start with a great blue card and go from there because blue is the best bridge color in the format. If you start in blue, you're going to be happy no matter where you end up, so something like Kitesail Corsair is an ideal first pick from a weak pack. The aggressive decks have gotten worse, but two-drops are still premium, especially those with evasion.
I would also take Merfolk Mistbinder over Impale, I'm generally happy taking a powerful tribal payoff over a removal spell. It's speculative, but you don't want to make everyone else's job super easy by gifting them a great tribal deck. At some point you have to plant your flag and that's way more difficult if the person on your left has already been dabbling.
Kitesail Corsair is what we in the biz like to call a "mythic common." If you see one past fourth pick, you're drafting with maniacs who don't understand how good a two-mana 2/1 flier is in this format. The fact that it's easy on the mana and has a relevant creature type makes it even better. Rarely, if ever, do I pass it in a draft; and any time I do, I feel like I'm losing or have done something wrong.
Deeproot Elite, in the right Merfolk deck, is completely unbeatable. It turns mediocre cards like Jade Bearer and Mist-Cloaked Herald into real cards that you actively want in your deck, and it turns real cards, like Jungle Pioneer, into unpassables. In my experiences, Merfolk decks have a very high ceiling and a very low floor. When they come together correctly, I cannot ever imagine ever losing with them. When they don't come together correctly - like a draft I did two nights ago - I cannot imagine dealing a point of damage with them (spoiler: I did not deal a point of damage in my two games before being kicked out of the MTGO League I was in because my deck was so bad).
I think Deeproot Elite is the best card in this pack by a fair margin, but Merfolk Mistbinder also being in the pack makes me really hesitant to take it. I don't think you ever want to be fighting over Merfolk in a draft. The archetype requires a lot of specific fillers, a lot of payoffs, and the failure case of the deck is really bad. When Merfolk comes together it is great, and if the other cards in this pack were a bit worse I would just say whatever and take the rare, but I'm taking the safe route here.
That leaves Bombard and Kitesail Corsair as the best two cards. Even if Deeproot Elite wasn't in the pack I would take both of them over Merfolk Mistbinder. Unlike the previous Luminous Bonds versus Bombard pick, this isn't close. Splashable removal is better than the best common two-drop, and Bombard is my pick here. Also to clarify on the other removal: Impale isn't splashable and costs four, and Hunt the Weak is basically not splashable due to it needing green bodies and also costs four. Both of those are worse than the Merfolk payoffs, with Impale being significantly better than Hunt the Weak.
If you've never been on the receiving end of Needletooth Raptor mowing down your entire team, consider yourself lucky. Once you have it, you should be looking to exploit the synergy with cards like Dual Shot.
Jungleborn Pioneer is simply fine, but moves up to great the more synergies you have with it. As is, Goblin Trailblazer and Waterknot are both stronger cards. Pioneer will merely clog up the ground while Waterknot and Goblin Trailblazer often dictate how the games are played out. Those cards should be a priority over filler.
Needletooth Raptor has one of the highest ceilings in the format, but its floor is major-pain-in-the-ass 2/2. That's my kind of card. Take it early, try to draft around it, and if you fail in drafting around it, still put it in your deck because it's still awesome.
Waterknot is similar to Luminous Bonds, even though it is a little rougher on the mana. Both cards are really good and you'll always play them. I'm never fist pumping when I see a Waterknot in a pack, but I'm never frowning either.
Oh, look. Goblin Trailblazer. What a lovely little Magic card.
Needletooth Raptor is pretty great. I think I still take top tier removal over it, but it falls into a similar category as Forerunner of the Legion but with more extreme results. You can always play it as a passable four-drop, but it just goes off the rails if you're G/R with fight spells and random ping effects like both Raging Swordtooth and Raging Regisaur. Even if you aren't G/R, any color pair can get the mondo-combo with Forerunner of the Empire, Needletooth Raptor is splashable in W/G, and even your U/R deck can just set up to play a Tilonalli's Crown.
Note that I said top tier removal, which doesn't include Waterknot or Impale. There are just a lot of double color commitments in this format that make them occasionally awkward. Both are still great, but they have a tangible downside. I still take Waterknot here over the strong two-drop of Goblin Trailblazer, with the red two ahead of Giltgrove Stalker due to a much better evasion ability and ahead of Jungleborn Pioneer because two is less than three.
Y'all are gonna think I'm crazy.
As I mentioned in Pack 3, starting with a blue card is ideal, attacking in the air is ideal, and picking up solid two-drops in blue is of the utmost importance. Cards like Impale, Moment of Craving, and Crashing Tide are great, but replaceable. It's also questionable how good those cards are on rate compared to a Welkin Tern in this format.
Everdawn Champion reads strong, but is a weak body and a mostly defensive card in a format where you'd generally prefer to be attacking.
My most common Pick 1, Pack 1 in this format has been Kitesail Corsair by a wide margin.
Moment of Craving kills my two favorite creatures in this format, so why aren't I taking it first? I'm not really in love with black in this format for starters, but I also just put a huge premium on elite two-drops as well. Kitesail Corsair and Goblin Trailblazer are elite two-drops and not the kind of cards I pass with regularity. That said, Moment of Craving is no slouch, as it's cheap, splashable (though not the kind of card I like to splash for as its power level is far behind Bombard), and lets you trade up the curve.
And well… Waterknot is Waterknot…
It would be difficult to get a clearer cut example of my common rankings than this.
First up is the single color cost removal spell. If you have been drafting for a while, you may have compared Moment of Craving to Sorin's Thirst or Pharika's Cure, but it is well ahead of those cards. Beyond the obvious doesn't cost double black, -2/-2 often lets you crunch a 4/4 with your 3/3 or something similar, where two damage would only let you one-for-two trade.
After that comes Kitesail Corsair, which is basically the only card in its class. The other evasive two-drops are good, but flying is just the best of the abilities they offer.
Then you have the solid removal that has cost restrictions. In a heads up pick I would take Waterknot over Impale for a couple reasons. Three is less than four, I like blue more than black, and often I find it hard to end up in black because someone took one of the four best black cards, like Ravenous Chupacabra, and never abandons it. In this specific pack if you for some reason didn't want Kitesail Corsair, I think there is an argument that Impale pulls ahead as you are passing a lot more blue of which several are good, but I'm not going to worry too much about that.