What about making only the pillars of your elements free?
And I defenitely agree with what is said here, you shouldn't lose your whole deck, when you lose, example:
When looking at water, we had some pretty good deckstrategies in our vault, but after losing 2-4 in the first round, we couldn't play them because half of the combinations we were thinking of, were lost.
What if we make the vault another idea, lets say:
250 cards before the bidding
225 cards after the bidding
Homepillars are free
When you lose you lose only half of your deck, rounded down.
The winner salvages 5 cards (meaning 3 wins fuel one loss).
The losing team DOESN'T know which cards are salvaged, and it doesn't influence, the cards they can keep.
This way, you don't have to use any combo's you made the first round, and you aren't that limited in you possible decks the following round, as you can chose which cards you want to hold.
But the seeding for the next round should be done AFTER each team has decided which cards to salvage and to discard, so you can't plan any strategies knowing your next opponent.