Well, the fact that Necropolis heroes develop Dark Magic against Orcs is obvious. However, whether they also get Summoning at the same time is debatable (it's quite possible to get both magic schools, but you still focus on developing only anti-Darkness magic). But what surprised me is that Necropolis isn't considered a rushing faction. Perhaps they haven't faced a situation where, after 3 weeks, they have Orson with 300 zombies and a Phoenix attacking the castle walls, and since Orcs won't get anti-Darkness magic that early (and even if they do, it's against Darkness), the chances of defeat are very high.