The magic system in Heroes V [Discussion]

I wonder, can a Warlock break the undead's invulnerability?:D

Unfortunately for you, Necromancers don't have intelligence, so how can you control them when they lack it? Defense and attack, probably, won't be a problem.

Added after 15 hours and 21 minutes
What do you think about this suggestion: initially, don't give any magical spells, let them study the corresponding school, then everyone will forget about improving unnecessary spells and characteristics without need.