Why not just remove GM all together. It's more trouble than it's worth.
Trust me, we could have such a cool system if there wasn't GM. It would be even cooler if we removed tiers.. But we could do a sweet tier system without GM aswel.
But yeah.. Some skills and spells need to be made not to work on GM's.. GM should just be a convenience, not such a scale tipper. Skills like brace that arn't available on spells or anything, shouldn't be available to any old GM.. GM's should just get spells and stuff that could otherwise be found on potions that are already out there.