Right now the Arena is a mandatory pointless, futile, effort: it is not PvP, not PvAI. It is AIvAI with P selection - it is purely a numbers imbalance, especially when some can afford to buy legends.
There have been many I could have succeeded in if I was selecting ultimate power targets. As it is heroes with backfield attacks don't always use them and if they do team doesn't react defensively.
Teams is fun but faces the exact same problem.
Just being to turn Auto off would be a massive improvement.
But the worst part is Defeat when time runs down due to healers. That should be a tie! Arena is sparring! If you can hold out against a stronger team that should count for something.