As you saw, the sideboard did what I wanted it to do: win games where we used it. Mindbreak Trap wasn't needed, but we also never had to play against Storm. Chalice of the Void won us multiple games on its own, and Rest in Peace beat Dredge singlehandedly.
Game 2 of round 4 is exactly why I hate Master of Etherium and Myr Enforcer against Pyroclasm. If you have those cards in your deck, are you just supposed to say go on turns 1 and 2? Do you really not put four points of damage in play on turn 1? I'm actually just fine losing to cards like Pyroclasm and Zealous Persecution, as they're underplayed in Legacy nowadays and the deck is capable of beating them. The heavy Memnite draws won't win against an early Pyroclasm, but that's why Magic is a fun game—sometimes you crush them, and other times they crush you. We played multiple games where our opponent resolved zero or one spell total. Our job is to create more games like that, not to try to steal back games where our opponent nut draws us.
After all, our Elves opponent managed to Therapy our turn 1 Chalice and turn 2 Tezzeret, Decay our Plating, and get Jitte up to four counters. They still lost. The moral?
If you're a nut draw deck, don't weaken your core game plan to try to mitigate damage from their best games. It's just not worth it.