Necromancer – “Invasion” [Campaign 3, Mission 3]

I didn't even have summons, and I managed perfectly well with Darkness.

As an option, but a well-developed Godric with antimagic can make the fifth mission very difficult. Also, with one stack + phoenix, you can clear almost all neutral creatures without losses and without using Raise Dead.

In the undead army, the Necromancer's "Raise Dead" leaves the raised creatures after the battle, and they don't disappear, but what about the Knight?

The Knight has excellent growth in combat stats and light magic, which brings undead into a combat-ready state, and nothing prevents the Knight from taking Raise Dead. And the Necromancer is a magical hero. His army should simply survive while Berserk, Dominate, Plague, Phoenix, etc. destroy the enemy. The Necromancer practically has no special abilities for undead (he is not a demon, dwarf, or orc). I'm not saying that the Necromancer is weak, but I'm saying that he is not a combat hero, and these are different things.