Hehe, good !
I can't help though for Marignon. For the matter of legion of steel and other spells being casted seemingly at random, it's true that it's strange. In one of my games, the pans actually casted legion of steel in on themselves when there was no units around them...
What are your armies made of ? Only centaurs archers and maenads ? Or also other kind of units ? It's very possible that since they cost (a lot more) the AI decides that the maenads are not worth protecting. In that case, using minotaurs and centaur "melee" units could make those protection spells target them instead. It's not a "fix" but it would help not wasting them. Another idea would be to use the centaur archers as melee units. It can work quite well in some situation, as I've learned when I scripted them on attack rather than fire, but centaur warriors would probably do a better job.