Right now I have concluded that the most powerful class in the game is, in fact, the Tempest-Rogue. Entirely because of something that is almost certainly an exploit, but which I hope they never patch, because I just find it hilarious to be able to kill a dragon in less than a minute.
Of course, I prefer to only use that on really hard bosses, or when the going gets too tough. I'm not trying to eliminate all challenge from the game, after all.