Well, you yourself readily accepted the idea that they could come up with a new unit, so I wouldn't dismiss the dwarves from the title of "4th faction" so categorically. It's as if dragons couldn't be replaced.

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although I don't even know which is worse: the dwarven faction from Heroes 5 or the orcs, who, logically and according to the plot, simply couldn't exist (if I remember the year of their creation correctly, although it would still be stupid, because there are no mages). And yes, for originality, they could have made the main faction not humans, but mages, for example. They created the orcs, and the necromancers originated from them. There are already two enemies, and if you add demons, it would be even cooler. Let them fight with everyone, because in every part, humans fight with demons.