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I still think it's not worth comparing SoD and VT. Tolyan even killed ГО on 115 playing as a Necromancer Castle, but that is a characteristic of the template, as well as +1 HP for skeletons in VT and troop experience.
In SoD, personally, I don't see any "mandatory" requirement for upgrading necromancers, unless it's Galtran, obviously. The example from a beginner's game only shows that both players chose such a gameplay strategy, not that it was the best choice in that situation. Damn, I'm getting confused with my commas already).
Even pros don't make the "best" choice! Because that always implies a giant risk. :)