Magic resist dealing poor damage isn't really the armor system fault. Enrage used to make mages ridiculous especially with enemies using them on you. Warfare buffed staff user getting enraged by an ally and using enrage on a boss was the highest burst damage in the game in EA.
They nerfed Enrage and made Flay Skin which is hilarious because the darn "Make magic deal more damage" debuff can be blocked by magic armor.
Create a new skill that reduce enemy resist like old Enrage and you will see mage damage become ridiculous again. There's only a single skill in the entire game dedicated to this role and it's used by a single boss, not the player. (-50% all resist and -4 con, goes through immunity)