I'm going to assume, for the sake of a standard, that we're discussing Submerged-level games.
Which is bad game design, and creates false dichotomies during character creation. One character type should not be able to edge out the rest. It's fine to have specialties, but wizards don't have specialties - they're amazing at everything between thaumaturgy and evocation.
Untrue. Wizards have specialties within and between those. It'd be rare to find someone who's "amazing" at both Evocation and Thaumaturgy at your basic Submerged game, and at that level, you don't get "amazing" in all sets of Evocation--not without neglecting something, such as enchanted items or defense.
There's very little that can be done to keep them in line. For example, you can't compel a wizard with 1 refresh to use magic to kill if he doesn't already have Lawbreaker - you'd be violating the social contract governing compels, it's exactly the same as if you tried to compel him to have an instantly-fatal aneurysm. You're being a bad GM and they have every right to call you out on it.
You misunderstand me. I'm not saying, after the fact, compelling a wizard to say, "Well, you hit that mook with a Weapon:4 fireblast, he's dead." I'm saying you compel, at the start of the scene, to say, "These are human mooks. If you hit them with anything Weapon:4 or higher, they're going to die from it." Then it's still entirely the player's choice as to whether or not he kills--but at the same time, it stops him from flattening a room with a zone-wide Weapon:6 attack.
Powers which can threaten a wizard's persistent defense rotes can roflstomp the rest of the party, so that's also a bad option. You're creating a new tier of play to challenge one character that other characters can't get in on.
Not necessarily. A couple maneuvers and an already-decent attack roll is good enough to get through most blocks.
A wizard is far tankier then the pure mortal standing next to them, because they can do things like create a 9-shift block that lasts four rounds.
Unless the wizard is purely Defensively minded, they're not going to be able to pull that block out without taking a solid consequence or spending several fate points. Which means they're going to be flagging behind on offense.
A wizard who can throw out a 12-shift spell on Defense without getting a consequence for it is going to need Focus items for it--which means they can't do the same for offense. And it means barring a good dice roll, they're going to be taking consequences just for casting in the first place.
And it means if they're throwing all their specializations, focus items, and skills into Evocation, they're going to be far from "amazing" at Thaumaturgy, and they won't have much room for Enchanted items if their shield fails.
Yes, a Wizard can throw out a lot of power at once but A. they have to
control it, too, and B. they're not going to be able to do everything on the same level.