I have no faith in Blizzard when it comes to balancing. WoW was a trainwreck for years. Druids completely dominated in healing and Death Knights in DPS for the longest time.
Balance is pretty good in WoW at the moment. The real clusterfuck of WoW balance has always been trying to get PvP
and PvE right with the same ruleset, which is almost entirely impossible, especially since it's a matter of balancing normal raids, heroic raids, 2v2, 3v3 and 5v5. They basically gave up on 2v2 balance which is just as well, it's not worth doing.
Jay Wilson has said encouraging things about not giving a fuck about PvP balance in Diablo 3, which is basically what I want to hear.
Then again, there is a lot more shit to balance in this game in terms of crazier itemization stacking, skill and rune loadouts and monster affixes. I don't expect it to ever really be balanced. It's not like D2 was ever
remotely balanced, I'll just be happier if they get it much better than that.
It's not really possible to properly balance very open-ended RPGs. PvE in WoW is highly balanced mostly because of how controlled it is, even so many MMOs have or had fuck-all for balancing.