A nation the AI could use *well*

[Aezeal]

Well how about just remove the gladiators from pythium.. it'd not make it less of a player nation and indeed the AI might be able to use the troops and those mages fairly well.

Maybe a nation like pythium with some death magic instead of astral or air (but that seems like ermor ) is AI good with MA ermor?

[Cerlin]

I find any medium infantry nation the AI does great with if it gets a good start. For example Formoria generally mixes well in my games with Giants and lots of firblogs. Also the Jotuns do great generally. I have also found the mod nation of Argus Dis does well as Ai even without the blood economies.
Easier Evocation magic, good national troops, less complex strats seem too be the winning combination. While these may be boring for humans and not great endgame without good pretenders, it still helps a lot.