Lol 20vs20 isn't fine imo.
Beggars can't be choosers...
What is wrong with battle? Many things. First, there is way too many ranged players and the objective of the game mode goes to their advantage (unlike siege where ranged is mostly useless). Team balance is broken, game constantly is shuffling players back and forth and every round you play with a brand new team. That doesn't help to fight banner stacks though, because those teams can be very bad in succession which leaves you with no multi. Rounds last a lot shorter than siege but you pay similar upkeep (even though you should pay less because chance is lower because of less time spent in round). There is no x2 for wins like in siege (bug? I love it btw). Maps are boring, the way you play the game mode is boring (survival). On the other hand, siege is dynamic, has meaningful goal.