Skeletons are the main part of the army (the Necromancy skill allows you to restore skeletons).
Well, they aren't exactly restored... Sometimes, such a "restoration" can be both a plus and a minus...
If you have the Unholy Cloak and the Necromancy skill:
Level 1 (Skeletons are restored)
Level 2 (Zombies are restored)
Level 3 (Liches are restored)
It will be difficult to argue against Necropolis with such advantages, not just for the Castle...;
Vampires are very useful in attack (they are restored when attacking living creatures).
Didn't you say that vampires are very weak?
The Veil of Darkness allows you to inflict darkness around the Castle within a certain radius.
That's a really strong argument :D
Halberdiers are the strongest unit of level 1.
Where did you get that from?
The Guild of Mages, level 4, is enough.
And why didn't you mention this for Necropolis? Maybe because they don't need level 5...? :D
Tavern upgrade, Brotherhood of the Sword (+2 to attack, when defending the Castle, I don't remember exactly).
That's not quite right. The Brotherhood of the Sword gives +2 to morale during a castle siege.
Heroes are really interesting and useful here.
And there aren't any like that in Necropolis...? :)