There isn't an option to allow the AI to cheat, I use the "No Building Requirements Option" and hide it so you cannot turn it off (if you want to disable this aspect you delete the Cheater Module). It is actually done by allowing you to build units which are exact duplicates of the higher Tier Magic users by using a building that requires the NEVER technology. Since nobody can ever get this technology, but the AI don't actually need the building, it allows them to directly build units that the player can never access
Glad to hear they were building Wizards, so far most people see them focusing pretty heavy on Summoning.
I'll be changing Fireballs & Meteors eventually I am pretty sure. But I wanted to see what other abilities I handed out before I did so. I am not sure if I will go with 0 visibility or with "cannot explore map" tag like I placed on some of my own summons.
You are correct, Barbatos is a world unit, thus only 1 ever spawns. I am contemplating making the other Unique Improvements spawn Unique Units as well, but I haven't decided on having a World Limit, or a Player Limit yet (one limits how many can EVER spawn, meaning it runs out eventually. The other limits how many can be spawned at a time. Meaning if you keep it alive then no more spawn, but the moment it dies more are available).
If I go with World Unit, then I really ought to make them immobile so that they guard their feature. And I don't like the idea of doing that too excessively, so I am thinking that I might make them a 1 or 2 unit Player limit so that they are out there somewhere, and can pop up and harrass you at any time through the entire game (but you will never suffer waves of them at a time).
If I stick with summoned units and assign a limit, then I am pretty sure it will interfere with summoning them, but possibly not, haven't tested that one yet.
Personally, I love making the Maelstrom spawn Sea Serpents. It puts some danger back into the waters

I ought to make it spawn the Black Wind though, and change it from World Unit to Player Limit (thus making it essentially an Immortal)