it's not so much about which classes are overpowered or what, victories are dependent on so much variables, including, but not limited to

a) who has first strike
b)equipment
c) skill & strategy
d) who manages mana better
e) potions or no potions
f) level
g) experience
h) environment

so saying one class is overpowered or not is quite a moot point to me, especially at this stage when WoW has already matured to patch 2.0.10