I'm not very comfortable with the argument that high-level wizards are balanced because high-level wizards don't actually exist.
This made me laugh and brought about a Monty Python D&D sketch to mind.
GM: Ok, now that Bob the Wizard has casted Locate Creature, Detect Magic, Clairvoyance you know that the Black Dragon is in his lair which is protected by a trap-filled descent down a sheer vent deep into the earth. What now?
Bob the Wizard: Ok, guys, sit tight in our cozy inn or go get a bear in the tavern while I memorize the spells; Teleport, Summon Monster (whatever), Invisibility Sphere, Spectral Hand, Greater Floating Disk, Shivering Touch and Animate Dead.
Group: .....
GM: .....
Bob the Wizard: Are they memorized yet?
GM: Uh, I guess.
Bob the Wizard: Ok, I teleport to the vent entrance, float down the trap filled vent, never touching the walls...invisibly...because yeah. Spectral Hand is ready to go when I get to the bottom. When I see the dragon, I Shivering Touch his Dex to 0 (no save) from waaaaaaaaaaaaaaaaaaay over here with my Spectral Hand. Summon Monster to coup de gras him so I don't have to get involved with that messy business and I can just check out the shiny. Oh crap. I forgot to bring Jack the Fighter so he could make himself useful by hauling up all of this loot on my disc. Oh wait. Nevermind. My giant undead dragon minion can do that for me. I Animate Dead this giant dragon because what self-respecting wizard doesn't have an undead dragon minion?
Jack the Fighter: Uh, the odds of you existing is pretty slim Bob. I'd say 1 in 1000000. What say you GM?
GM: You know Bob, Jack is right. Let me roll percentile dice. On a 100 you exist. Drat, 42. Poof. You don't exist. Alright, the rest of you guys, what do you do about this dragon that you don't know where is nor know anything about his lair?
Group: (In unison) WHERE IS THE MERCHANT IN THE TAVERN THAT WANTS US TO GUARD HIS CARAVAN ON THE BANDIT-INFESTED TRADE ROUTE?