AI in Might & Magic: Heroes VI

Maybe he's just better at the game?

or he had good artifacts.
For example, the Guardian's Breastplate, in my opinion, is the most overpowered artifact – the first three attacks on a unit do no damage to it.
Once I played in a skirmish, and in the final battle, both I and the AI had this artifact. It was a complete mess, not a battle. Especially considering that the AI was a Demon. That is, it attacks me and does no damage, and its luck triggers, and it summons reinforcements, against whom the first three turns also do no damage. I lost badly, although the threat to me was moderate, that is, our forces were roughly equal. I had to replay the map.