I noticed a possible exploit. In War #2, Aether had 59 cards going into the next round (1 more card means we field two players). It was possible for me to substitute for Icecoldbro and win, thus keeping us at 59 cards. However, the only event stopping me from doing this is the lack of upgraded cards to play. If upgraded cards were allowed use, then one team can field the same deck forever by somebody who isn't their General, especially with 70 cards to work with in War #3.
Yes but with the same 59 cards every round, wouldn't it be pretty difficult to keep winning? I mean your opponents will pretty quickly learn what cards you have and destroy you.
The same principle could apply with more cards though, with 89 cards you could sub every match and keep 3 decks, your opponents would know your vault but you would have enough variety to avoid being countered.