Arena can be more balanced if they introduce a ban system and coin system.
1) Ban the passive barrier guys, cause it's really unbalanced (and maybe someone else too like super rare ninjas)
2) Coin or roulette system: a simple roulette or a coin flip to decide who starts first, but no the entire team, exemple:
A vs B
coin decide that A starts so then:
1st position A will attack before 1st position B
but, 2nd position B will attack before 2nd position A... and so on.
I think this is the fairest way, more fun, more strategy, tactics. Cause it's frustrating to see that whole enemy team is faster than mine while arena should be fair, cause right now there's no point to put lvl 100 to everybody if the system still calculating second attributes from original stats.