I think you're overrating Mental Toughness a bit. It's certainly worth its cost, but the sort of shift-counting that you did there is going to give you a misleading impression.
Ignoring backlash like that isn't a good idea, and the measure of a wizard's power isn't the number of shifts they can put out in a scene. If it was, a guy who could cast power 1 control 1 spells for free would be better than the whole Senior Council.
I fail to see how you'd practically compare the powers in another way. I pretty clearly hedged my statements with the fact that I know there are flaws in the analysis, and what those flaws are, but there are always going to be flaws in any analysis. I'm looking at situations when you're going all out with your magic in a prepared fight where you've got the FPs or Maneuvers to weather most of the Backlash. If I'd more optimized the Focus Item assumption I made, the contrast between the powers would have become even more stark; a +4 to control offensive spells would have introduced another 4 shifts extra from MT vs SF, and if we compared defense it would've been 13 shifts extra from MT vs SG, and quite a bit less Backlash to boot. Mental Toughness obviously is less OP if you're not using it to its full extent...like any power would be. If you don't stretch both Soulfire and Mental Toughness to their limits, you can't get a practical comparison at all, short of running the exact same conflict twice with the only differences being the magic user's sheet, which still would see no practical possible differentiation until each PC was stretched.
I think you're overrating your assessment of my assessment a bit; I'm pretty sure I've got a great impression of Mental Toughness's power, whether or not you agree with it. A measure of a wizard's power is LITERALLY the number of shifts they can put out in a
practical scenario with
reasonable assumptions. It is practical to assume there might be 6 exchanges in a conflict. Your counterexample is farcical and insincere; you can't assume most fights will go for hundreds of exchanges, which is what your scenario would require to balance--and that's assuming the non-single-shift caster's opponents are somehow tied up and can't act. Even if the Senior Council were totally out of magical gas, they can do things like punch and throw things and move around, and presumably these aren't all at Mediocre or Average for all the Council; Weapon: 1, 1 to strike spells forever is obviously weaker than even a normal spellcaster, let alone vs SF or MT, and using my comparison method would prove it HANDILY if you deigned to consider it properly.
This is the only way to compare two different sets of powers: how many shifts are you getting out of one versus the other, in the same situation? If it is not, how could you possibly make an objective argument regarding the strength of one power versus another? You'd simply ram opinions around, otherwise, and while there's plenty of room for opinion in an RPG, there are also definitely situational advantages one power will provide over another, demonstrably making it a better power for that set of assumptions.
If it were not, why is magic considered so powerful in DFRPG? Sure, there's room for doing impossible things you couldn't otherwise accomplish, but practically speaking that rarely really gives you an advantage you couldn't have created another way. The strength of magic in the system is obviously the fact that you can achieve incredibly high weapon damages and rather high Blocks and Maneuvers compared to most PCs. The most significant limit to this power is the clearly limited number of times you get to perform a spell in a conflict. When you take that limiting number and increase it by
fifty percent, you've suddenly
dramatically changed the effectiveness of that limitation.
Even if we applied Backlash shifts as negative shifts towards the total instead of ignoring them, you get:
Mental Toughness, Apex: 95 shifts
Soulfire, Apex: 64 shifts
48% more shiftsMental Toughness, Non-Apex: 62 shifts
Soulfire, Non-Apex: 49 shifts
26.5% more shiftsEven if we were to allow for Soulfire users performing two actions when the MT-user has those two extra spells, to be completely even in the assessment, and assuming they have a useful skill to use at Superb, that's only 10 shifts more--you're still 3 shifts lower w/ SF vs MT in the non-apex situation. If you use those two actions to maneuver with Discipline for a +2 to control two spells, you've just now beaten MT in a non-apex situation by something like 9 shifts...but only until you use more optimized Focus Items or use a lot of defense, and then once again MT comes out on top. So in all situations you might run into where your magic is strained, except non-optimized non-apex casting (pretty uncommon...), MT comes out on top--and most of the time, significantly on top.
I realize I'm in the minority regarding my opinion on Mental Toughness and PCs, but that's why we all have our own sandboxes.