I don't know how much the third map in the campaign has changed compared to its single-player version, but in my opinion, this single-player version is the author's best work in terms of balance. It can be completed with seven out of eight heroes (if there were at least some way to obtain summons, it could be completed with Gothai as well) using a wide variety of builds and in almost all scenarios. Perhaps the difficulty drops towards the end when the mentored Isabelle starts churning out horses, and both Udo and Khan are easily defeated by 200+ paladins with vampirism. In short, no nerfs are needed...