Miscellany: The D&D elephant in the room

We're approaching the level in our "Red Hand of Doom" Dungeons & Dragons campaign where the game starts to unhinge. More specifically, it's as if the ghosts of D&D game systems past come back to haunt the players, their fetid claws wrapping around our play sessions like shackles. I'm talking about the wizard (or spellcasters in general, but the wizard is the best example).

At the beginning of the game, the wizard is dramatically underpowered versus all the other character classes, even the spellcasting ones - he has much worse fighting ability and hitpoints than the cleric, for example, while possessing less useful spells. In an adventuring group, he has little to do at these beginning sessions but shoot at stuff with a crossbow and hope for the best.

Around 7th or 8th level, though, you start getting access to spells that allow you to do almost anything - fly around like a bird, convince enemies that you're their best friend, or even create stuff out of thin air. In the hands of a skilled player, the wizard can essentially annihilate any enemy. Compared to more mundane classes, like rangers and fighters (More favored enemies. More bonus combat feats. Yay?), who can really only swing their swords better at higher levels, the difference in variety of play is grating.

It gets even worse at higher levels. Wizards can now kill people with a word, take extra turns in combat, and reroll the dice. To an outside observer, it must look a lot like cheating. I'm not sure how to rebalance D&D so the "tanks" get more to do, but from everyone's experience with the D&D wizard, I do know that being able to alter reality at will has a tendency to make a class overpowered.