It's not that Control mirrors are a problem, but the fact that a single card RNG effect is the de-facto decider for the winner, in Warrior vs Warrior mirror in particular. No wonder people are teching Baleful Banker in the competitive format, as that single act decides the winner. There's also Hecklebot, which forces the game to be decided by who can pull the opponent's Elysiana or Baleful Banker. This doesn't make for very compelling competition, just a RNG clownfiesta.
On ladder though, it's just annoying. If Elysiana's effect where somehow more predictable (as in, the discover has a more particular rule, e.g. first choice is a 5 mana minion, second is a 5+ mana spell, etc.), and restricted to only once per game, we could at least take out this exaggerated RNG factor from the outcome of a game. But alas, this may also end, if we find a better control deck (unlikely), or if a counter combo deck arises (probably Malygos Druid).

And I say these, as a CW player, just like Zevox, that wants the game to be decided by my decisions overall. RNG is ok, but not when it's this decisive.