Lord of the rings battle for middle earth 2 computer hero spawn on xbox 360?

Mk so like i love gong against computer that's in the castles like for instance helms deep my favorite one but every time computer starts in a special fortress, they do noting but spawn heroes and build recourse buildings, i mean im just like wow this sucks its so boring,so if anyone can tell me if that's just the game or im just doing it wrong plz tell me.