Support team battle rules could be a separate pvp event which has beneficial output to main team.
Support team deckbuilding rules suggestion;
Rule 1) 50% must be in-element. All cards unupped.
Rule 2) Support team members can use any card except shards.
Rule 3) A support team member cannot use a deck which has half of the same cards (non pillar/pend) with any of support team's earlier decks.
Rule 4) No rule 3 restrictions for 100% mono decks.
So deck building of support teams will be entirely separate. Support teams will be forced to be innovative due to rule 3 or just repeat mono decks which has a better feel for the elements-war. The rule should act like a loosely ruled vault. IE; every support team can use a good grabbow, then a mediacore grabbow, then a crappy one or unable to make it at all. I didn't build decks to test with this rules but this way support team should be able to build good decks which are not repetitive.
This is only about support team deckbuilding, not the matchmaking rules or the rewards.