Really funny. In this thread people say arena matchmaking IS done by total account power - and that would be the main problem of the game, because getting better champs for your Clanboss team would increase your account power and therefore result in harder arena fights.
In this thread SevarD said the arena list depends on your level and this is supposed to be a problem - and according to G0lc0nd4 the way to solve the problem would be a matchmaking based on account power.