I only have 1 standard hero - Naadir is being developed in a standard way:
1. Darkness
2. Summoning with mines
3. Leadership or defense, if things don't work out
4. Education
5. Wizardry
23-25 lvl IMHO, this is already decent, the Necromancer will have such an army that 5 fireballs won't save you. Against the Necromancer, the Dwarf will definitely shine. Runes don't seem to remove plagues.

It seems you've been playing on the computer too much (no offense)!
I have a lot of experience playing as Dwarves against Necromancers and against quite strong opponents, here is my classic build against the Necromancer, whether he has Darkness or Summoning, and considering that he has two castles:
Helmar (up to level 25) Perfect Knowledge of Runes, Greatest Rune
1. Constant Luck: soldier's luck, magic resistance, dwarven luck (let's see what percentage of your spells will be able to affect my units - check it and you will be very upset, I guarantee it);
2. Skilled Light Magic: righteous wrath, storm wind (try to fly); you can take blessing instead of one leadership;
3. Skilled Leadership: runic harmony (if there is no retaliation, we may not take it);
4. Skilled Defense, but if there is a resurrection rune, then evasion and damage reduction;
5. Skilled Attack: tactics, attacking hirdu, retaliation, but if there is a resurrection rune, then the build is like in point 4;

Try playing at least once against someone who knows how to play as Dwarves, and you will understand that in reality, the Necromancer has no chance, no matter how you develop!

P.S.: Runes remove any spell!