RPGMemes

A tale as old as time: the linear warrior, quadratic wizard. (TVTropes warning.)

I think it's a problem just because of changing expectations for the game. If you're playing modern D&D, where combat is supposed to be balanced, character death is rare, everyone levels at roughly the same rate, yeah, it sucks to be an early level wizard or a late level fighter who can't keep up with the rest of the party. I get why the trend has been to try to balance them, even if it's a bit wonky. I get it, it's hard to do.

But if you're playing it in more old-school way, where it's more gamey, it makes a LOT more sense. Combat isn't necessarily balanced, character death is more on the table, you're more likely to have a rotating cast, and parties can have different levels between the members. So the late-game magic-user is the reward for playing the class that's weaker earlier on, and the fighter is great for jumping into the action.