Hypothesis: Anyone complaining that magic-users are too powerful in comparison to other classes-- especially fighters-- has never played an old school magic-user.
Why do I say that? I find it hard, hard, hard to believe anyone would complain if they had actually experienced how hard an old school MU has it. Hell, one of my players has a MU with 1 freaking hit point! He's already died twice and only lives because the party encountered a time travel tower. And, because it takes so many more XP for him to level, the fighters are all 2-3 levels higher than him.
He has to hang in the back of the party (but not the rear!) because one hit will kill him. He has to bide his time because he has only one spell to cast. The time he does cast it will be terrifying because it means there is something the party's multiple fighters couldn't take out.
Will he be more powerful than the fighters come 8th level? I damn well hope so.