With heavy armor, he also isn't that great of a pack mule since he can't carry that much.
He still only uses novice and apprentice destruction spells in combat, though. When I took J'zargo as a follower I gave him extra magicka on his gauntlets, extra regen on his armor and helmet, elemental resist on his boots and a combo of elemental and magic resists on his necklace and ring. They can use resistances, stat increases and extra regen. Player can also change spouses outfits by giving them weapon/armors via dialogue.
Also, most followers(maybe all) cannot take advantage of fortify skill enchants as only the player has a special hidden perk that allows you to use them. PS4/XBOX/PC How mod improves game play Makes the game more immersive.
NPCs don't care about enchantments, they only care what a piece's armor rating can do for them. At higher levels he has high to max heavy armor skill and will gladly equip some nice high quality heavy armor(well tempered and enchanted is best). He has no level cap(if you are level 150, so is he). I have taken J'zargo as a follower, though. I can't speak to Aranea as a follower as I've never taken her as one.
