Necropolis and Demon.

It all depends directly on the player. Let's start with the fact that it's not difficult for a Necromancer to defeat a Demon hero if they develop along the chain for the "Shriek of Horror" spell. We upgrade summoning and all related skills up to the "Banish" ability, and the Demon Lord's main advantage fades into the background, as it no longer poses a threat. Furthermore, even before opening the gates, the Necromancer can significantly reduce both the initiative and morale of their opponent. If the hero is not human, these characteristics can be reduced to -4 or -6 (at least for morale) without using "Shriek of Horror." Thus, we get rather helpless Demon troops with a very strong hero. But the victory will undoubtedly be on the side of the Necromancers.
Another model: for Demons, the most important skill is Logistics (I won't talk about attack, as it's obvious). If the player controlling the Necromancer is quite experienced, they won't miss the opportunity to take advantage of all their hero's advantages. Then, the recipe for the Demon that will level the playing field is: Readiness, upgraded attack, and Surprise Attack. If the Demon Lord has an advantage in troops (even a small one), then victory will be his.