Auto-translated
I don't quite agree that 3 schools of magic are too much for a Necromancer. Actually, in this campaign, we are playing against heroes who are very skilled in chaos magic – wizards and demons, so my primary goal was to weaken the enemy's magical attacks as much as possible. So, you can develop your character effectively as follows: take defense, level up the reflection perk (-15% of enemy magic attacks), then take wizardry, level up to "Secret Knowledge" and get the undead protection from magic perk, which is another 20% reduction in enemy magic attacks, and here is where chaos magic comes in handy, where we level up to Storm Lord and get the magic depletion perk, which is another 20% reduction in magic attacks, so in total, we get 55% less damage from any offensive magic, so choke on your magic wand, you lousy mage:D
PS By the way, alternate-greyed skeletons have 25% magic resistance, so under all these perks, the skeletons become almost like golems, which magic doesn't affect at all).
Well, here's another option outside of campaigns (in very large generated maps): I took a combination of Education + Wizardry for Necromancers, by the way, including against dwarves, but this is not enough in the long run. But within the campaign, it's quite good. And by the way, the well-known "weak point" of Necromancers is the almost complete lack of attack stat growth, but if you take and develop the Attack line, it is hardly noticeable. But as an option, say, due to Ranged Attack.