Are Wizards Overpowered

This a question akin to asking whether your offensive lineman or your running back is more 'powerful'. They've each got a role to play and the team works better if they're both doing it.

If you're playing a level 20 one-shot, perhaps the single most powerful ability in the game is the origin feat Alert - coupled with a Dex-based character who generally has additional Initiative bonuses. Being able to pick who goes first is enormously important because you'll be facing enemies that incapacitate almost anyone in your party before they can even act.

However, "Alert guy" - the guy who invested all that effort into a high Initiative roll - is rarely the one you want going forward. A Dex-based Battle Master isn't likely to strike down Vecna with a single blow. But he's likely to be able to survive whatever Vecna can do because he's got hit points, AC, saves, etc. In contrast, that Wizard has all sorts of tools to shape the battlefield - tools they'll never be able to use unless they can act before Vecna does.

Think about how an Arcane Trickster and a Wizard dovetail well together. The Trickster can burn through Legendary Resistance at an exceptional rate due to Devious/Improved Cunning Strikes. Then they can take a scroll the Wizard scribed - using the Wizard's spellcasting ability and spellcaster level - to throw an offensive spell that the enemies will be forced to save at Disadvantage. The spell itself is dependent on the Wizard, but the Rogue is setting it up to make it useful.

So while it might make some sense to ask "How do a Wizard and a Sorcerer compare at filling the role of the pure caster?", it really doesn't make much sense to compare a Wizard and a Fighter - other than to note the obvious that Wizards suck at being Fighters and Fighters suck at being Wizards.

I personally think Wizards are one of the worst classes. Sure you have lots of versatility with spells, but in game play you have to deal with concentration which means you can have one defensive/utility/condition spell and then just toss damage spells. Get hit, lose concentration, lose a spell. With very limited spell slots that can hurt a lot. Secondly, at high levels you run into a fair number of enemy bosses who all can auto save, so no powerful spells or they just auto save. Want to learn more spells, spend a ton of money. Also several spells cost money to cast. Want to be a diviner? Cast divination and spend 25 gold each time. Compare to other classes and to be equivalent they would have to spend money to use their powers, would have enemies that just say "You auto miss". Get hit and you have to make a concentration point or lose your actions. Etcetera. Having now played a high level Wizard I would never play one again.