Which faction poses the greatest challenge for the Dwarves?

Zombie Peasant, what are you talking about? Why would I constantly cast Dispel? Dispel is only used in response to Necromancer hero's curses. And since it's a general spell, the next cast will be mine again (if yours is a single-target spell). "Unholy Word" still needs to trigger, and artifacts are a matter of luck, so why guess?

And most importantly, if people here are confident in the strength of Dwarves (and there are several of them), and you don't see their strength, maybe the reason isn't us, but you?
Leadership for Necromancers? Well, that's debatable, to say the least. Maybe only for the Mine Dweller, but in any case, it's not easy to get, and it's clear that it's unlikely to happen at the very beginning.