What does "aggressive AI" mean? There's easy, medium, and strong AI. By the way, in your first message, you mentioned "against 5 complex AIs," but there aren't any; you must have confused it with "5 strong AIs"?
I see several advantageous points for the Sanctuary:
1. For all factions, the weekly growth of skilled creatures in unupgraded buildings is 1, but for Kirins, it's 2 (this is a significant advantage). In upgraded buildings, Kirins grow by as many as 3.
Basic building - 1 unit. Upgrade +1 unit. Fort +1 unit. Citadel +1 unit. Castle +1 unit. In total, in 1 standard city, there are 5 skilled (champion) creatures.
So, we're back to Heroes 2 and 3, where various high-level monsters – dragons, titans, and angels – unequivocally ruled.