Now, there is one flaw in this logic. Well, other than everyone should, in theory, try to win, not just skip turns waiting for the inevitable end. What you should and what you shouldnt is not defined indeed.
Let me try to explain.
1) Nobody likes to gang on Ermor, especially early in the game, because Ermor is damn hard and it dominions makes sure you will only get wastelands after all your (wasted) efforts.
2) Unchecked, a well-played Ermor almost invariably becomes one of the major forces.
3) Usually, there's another well-played strong nation.
4) They declare war on each other.
5) If you fight a well-played Ermor alone, you are more or less doomed. Any losses you inflict on him, he just shrugs off as more undead rise from the graves. 200, 400, 600 undead killed in one combat mean nothing to him. Any losses he inflicts on you are painful. And its hard to counter darkness + rigor mortis, you know... because solar brilliance, the only counter to darkness, also blinds your own troops making them useless. And its harder to cast.
6) Most likely, Ermor will emerge victorious in the end. And nobody else will be in a position to challenge him, so its game over.
Against any living nation, you will stand a chance because its a matter of diplomacy and skill. Against Ermor, when he kills his only rival, you can only give up.
I have tried explaining it in another game, and was laughed at. Well, lets see how you laugh when Ermor kills Dimaz.