Compels are not bad. If you compel a capability away from someone, they still benefit from that capability.
So as a way to make characters weaker, compels don't work at all. You can't fix a balance problem with compels.
Compels are useful for precisely that reason.
We're going to have to disagree on that one, I suppose. Compels can't only make a characters life complicated, they can, as a teamworking tool, be used to push a character into the backseat.
For example: a group wants to enter a building unseen. The wizard immediately jumps up and proposes a veil to sneak in. So far so good, but a creative player can make his wizard do almost anything, and he would leave every other character in his dust. And here's where compels come in. You (or maybe another player) tell the wizard player, that his magic would interfere with revolving doors, cameras, motion detectors and what else have you. He would get in unseen, but the place would be swarming with security regardless. Here's a fate point for your trouble, let someone else take a turn. Someone else, a spy type character for example, can take the wheel now.
If you do that evenly around the table, each character will have a time to shine and a time to lay low. And he will have a handful of fate points to tap into his full potential.
That would be my personal view on balance, at least in this game. What is yours? Where would you like to see a wizards power to be? At the moment it just feels that you think they are incredibly overpowered and need to be killed with a lot of fire. If I knew where you want them to be, I might be able to follow your reasoning better.
Maybe an approach to a new building block evocation system. The idea is to make magic work almost like any other skill. I think you've done something similar with claws and breath weapons. It is a work in progress.
The Basics:Each of the basic Spellcasting powers grants 1 Element to do your spells with. Once you have an element, you can use it on every magical action you know, so you will not have to buy all 3 powers for each element. None of the basic spellcasting powers use casting stress.
Magic Attack [-1]:
You are able to do magical attacks. Roll your discipline as a ranged attack with a weapon rating of 2.
Magical defense [-1]:
You are able to use your magic to block attacks. Roll your discipline to put up a block. The strength of the block is equal to your roll.
Magic Maneuver [-1]:
You are able to do maneuvers with magic. Roll your discipline to put up an aspect.
Upgrades:These Powers require their basic counterparts to work.
Powerful Attack [-1]:
Your magical attacks are more powerful. Add +2 to your roll, when doing a magical attack. To use Powerful Attack, you need to take 1 shift of mental stress. (I know, usually it's +1 to add to an attack roll, but with the stress cost and the fact that it is a power, I think it is ok.)
Potent Attacks [-1]:
You can do magical attacks for an additional 2 shifts of damage. To use Potent Attacks, you need to take 1 shift of mental stress.
Massive Attacks [-1]:
You can use your spells to attack an entire zone. To use Massive Attacks, you need to take 1 shift of mental stress.
Potent Maneuver [-1]:
Your magical maneuvers are more powerful. Add +2 to your roll, when putting up a magical block. To use Potent Defense, you need to take 1 shift of mental stress.
Potent Defense [-1]:
Your magical blocks are more powerful. Add +2 to your roll, when putting up a magical block. To use Potent Defense, you need to take 1 shift of mental stress.
Lasting Defense [-1]:
Your magical blocks last 2 exchanges (for a total of 3 exchanges) longer, without freshing them up. To use Lasting Defense, you need to take 1 shift of mental stress.
Additional Element [-1]:
You can cast spells in one additional element.
Focus Item [+1]:
You can attach part of your magical powers to a focus item. If you lose that item, every roll you do for those powers will be reduced by 2, until you recover or rebuild the item. You need to attach at least 2 points of refresh to benefit from the refresh bonus.
Enchanted item [-1]:
You have 2 free uses per session for any evocation power that would normally take mental stress to use. This power may be taken multiple times.
You could even take other skills for the 3 action types. Maybe weapons for attacks (throwing fireballs) or conviction for maneuvers. Would probably be best, so wizards don't rely on only one skill. Maybe even different skills for different wizards, depending on their style, as long as it's three different ones.
If you want more powerful wizards, you can let them take multiple Upgrade powers of one kind and let their uses stack. But if you only take one each, a wizards power should be manageable and on par with other templates. Maybe even a bit weaker compared with speed, strength, etc.
Something similar could be done for thaumaturgy, but I'll need to think a while longer on that one.