A simple (not mass) exorcism spell by still limited spellpoints would be nice and adequate.
Spell point draining does not fit well to might. This fits better to necropolis. But making spells cost more could fit.
The most important thing would be the general magic resistance of might creatures. But if possible this should include resistance against beneficial spells as well. A 25% chance seems appropriate.
Higher ATT values seem reasonable, too. Higher DEF values not. Maybe increase Hitpoints.
BTW: Anti-Magic could be another nice spell for the Ogre Magi. Dragon strength and Mirth too. But the spell points should be limited so they can't cast all of them. Maybe just one Dragon Strength or two others.
REM: If the Ogre Mages had these spells, consider this combo/scenario: Barbarian has a Behemot stack and three Ogre Mage stacks. The Behemots first wait. The opposing Mage does some magic on the Behemots. Now the first stack casts Exorcism on the Behemots (or places itself directly in front of them if berserked), the second casts dragon strength, the third casts anti-magic. I think then the mage is toast
This would be the perfect counter to a strong magic hero.