Do you mean Foul Air, or Dark Skies? -very- different effects; the one you described (morale loss for enemies in caster's dominion) sounds like the latter. In any event, with your gem stash, why haven't you dispelled them ?!?! Use alchemy to astral and empower if you must.
With that kind of province disadvantage, you probably need to wreck temples en masse before you get overwhelmed by hostile dominion. Remote summons can be good, although the air/nature ones aren't that strong (compared to Conj 9's Ghost Riders, for instance, which is a decent raiding force, and Army of the Dead, which is a nice followup).
Masses of unbreakables will also help neutralize the whole point of dark skies. Many magical units are mindless and unbreakable; at that point, you just need to make sure the mages won't rout.
Wish would be nice, heh; it's hard to rout a Doom Horror.
