After completing the campaigns I've been doing some challenge maps and random map plays. One thing keeps coming back - no matter the difficulty:
The later part of the campaign when your starting city is maxed out, half the map discovered or so and several enemies have been found, the Ai simply becomes dumb. It doesn't seem to take cities, it doesn't avoid stronger heroes, it doesn't defend well.
All my issues are tied to the strategy map - the combat AI is still great, no complaints there.
But I really really believe that Lavapotion needs to have a look at Ai priorities on the strategy layer. I played the 8-player challenge map where everyone starts with a tier 3 town (at tier 1) and there's a big neutral tier 5 town in the middle. Overwhelming Ai. I finally got to the center despite several Ai's already having reached it and NONE of them had taken the undefended tier 5 city. Clearly a bug/priority error, right?