I know SP games don't give a valid image of what could be the actual strenght of some tactic - one could be easily counterable but the AI just doesn't know it.
But, just to say, in my last SP large map all nations game the Poison Golem Idro was at the top of the Hall of Fame with some thousands of kills, having taken 3 or 4 nations all by himself with the obvious exception of the castles.
He just fell attacking more than a thousand Marverni chaff army - when the enemy was already routed, he died for turn limit. - (Now NTJedi if you are reading, don't gloat ^_^ I still like this mechanic as it is. I would just have needed more firepower, period. Somewhat annoying maybe but surely fair)