My concern isn't if Iron Man can take out the minion - of course he can with an apex skill of +5 vs the minions apex of 1 to 3 (the guy with the 3 might be carrying a bazooka).I totally understand the concern re: Iron Man's Resolve (didn't Hemingway write that?), and I'm aware this needs tweaking -- possibly past the point of recognition, but that's how these things often go. (I'm less married to the scales than to the player-defined super-skills-plus-trappings thing.)
With different scales as you have proposed where you either need to buy into the scale or spend will to temporarily act on that scale. My concern is more that Iron Man forgetting to take his Resolve to the super scale and Psychic Blast dude with a Fair super scale mental attack being able to casually mop the floor with Iron Man.
First thing I'd buy under your system is a super defense in every conflict category (probably Endurance and Resolve). And when everyone needs to do something like that to "feel playable" then IMHO something is wrong.
My concern with removing the scales, or redefining what Superb means based on genre, is that within the supers genre abilities can vary so wildly I'm not sure a scale of +1 to +10 would really cover it. And once we get up past Superb, it really bugs me that the character's bonus far outstrips the variability of the dice. I admit it is more intuitive to just say "I'm the Hulk -- I have +10 Super-Strength!" but the +10 itself puts me off.
This reminds me a bit of something that came up for Legends of Anglerre. When we were tossing around ideas for epic-level characters, an early one someone proposed was the idea that you'd spend spin on an attack to do something extra, or to have an effect -- like spending spin to be able to harm a dragon -- but all that really boils down to is a +3 to the defender's defense. LOA still makes use of spin for epic-level stuff like that (last time I saw it -- who knows what it looks like after editing?), although the problem remains that equally matched high-skill opponents are no more likely to get spin on a roll than their equally matched low-skill counterparts.
That's the kind of thing I want to avoid, and am struggling with (or "with which I struggle"). I'm not comfortable with the Hulk having Superb Might while a mook has Average Might, but nor do I like expanding that range out ad infinitum to accommodate those extremes. I really want the split between Human and Superhuman to be more than a few degrees' difference on the ladder. I fervently believe there's another option, and if separate scales isn't the solution, then there are other switches and dials still left for me to fiddle with.