It should also be noted that it is desirable to keep the vampires. With blindness, they will easily deal with the knights.

The knight takes down the vampires first.)))

It is very important for the knight to have teleport! Act only on attack. Throw all the fighters into the thick of the enemy (otherwise, the necromancer will outnumber them, and they will kill each other). Of course, ideally, you should have the Shield of the Dwarf King.)))
In my opinion, these are the best upgrades for the knight:
1. Landlords (they have higher attack and can attack twice).
2. Archers without penalty (needed to take out vampires; the necromancer still won't get close enough for the archers' ability).
3. Zealots (send them into the thick of the enemy and hack, hack, hack).
4. Royal Griffons (attack from the sky, stay on the field for as little time as possible so that the necromancer doesn't control them).
5. Red Adepts (again, focused on attack, also have a very important spell and ability - dispel).
6. Paladins (if you have the Shield of the Dwarf King, you can also consider knights of Isabel, although the paladins' ability is very valuable).
7. Archangels and only archangels (stable damage + resurrection of allies. Divine Retribution is still not needed, since the necromancer's main striking force is the necromancer himself, not the necromancer's troops).