I see this as a flavor versus rules argument. No, really I do.
The idea that a wizard just gets a spell is ludicrous in my vision of how magic works in a game world.... but that's my vision.
I have a buddy that feels that auto spells equals experience and "off camera" study during the level gain.
Either is certainly workable, neither is perfect, and like most attempts at a Vancian structure, it never will be, but that is part of the charm of D&D. As I've gotten older and more or less wiser (or at least just less worrisome over certain things) I realize that I don't love D&D despite it's warts, I love it BECAUSE of it's warts.
Wizards should not wear armor and should be walking targets until 5th or 6th level, then they should start to out class the characters around them. The trick is, they have to stay alive in order to get there, and frankly, it shouldn't be that easy. When a kobold armed with a stick or a rock is a serious threat to a low level wizard, then all is right with the world.
Likewise a fighter should be cock of the walk until about 5th level, then he should be a meat shield. The cleric should be a mobile defensive healing machine and a thief (rogue) should be quick, stealthy and level faster than anyone else (because otherwise they get left at the gate very quickly).
Is it perfect, no, but it's what I want from D&D, if I want balance I'll play GURPS...and I don't play GURPS.