The fact that it is balanced for play is all that matters.
That is not relevant to whether or not power creep is occurring. Are many of the new classes balanced for play? Yes. Do some of them represent power creep in the game? Yes.
If you don't want to believe the warlock can be situationally more powerful than a wizard or sorcerer, I'm sure you can elucidate us on how a swordsage can often be more powerful than a fighter.