I'm going to come clean on something here. For years now I've not seen much force to the complaints about game balance vis-à-vis caster classes and martial classes, even granting that 5e has plenty of imbalance in that area. Assuming all party members are working together and prefer working together instead of against each other, why should it really matter so much that one player can do lots more than another so long as all players consistently get to make important, meaningful contributions to the adventure's progress? I used to play characters who were four or five levels below other players and never minded doing it. To me, actually, it kind of made the whole thing more fun, you know? My thinking was, "Okay, so here I am playing a guy like Pippin while Jeff is playing Aragorn, son of Arathorn; this is awesome!"
In 1e, we regularly had some players advance much faster than others just on account of the fact that gold pieces converted directly into experience points. None of us objected to that; we found it plausible and helpful to the overall story.
So let's just grant the premise that Wizards are OP when compared against Fighters. So what? So long as they aren't so badly overpowered that no one ever wants to play a Fighter anymore (and in my group, anyway, we've not had that problem), what's the big deal? Balance, schmalance: is everyone having fun? If the answer to that is "Yes," then I'm satisfied.