MMH5.5 - Heroes of Might and Magic 5.5

And I also don't understand the need for necromancy for all the dark classes. Maybe it could affect morale and stats?

Yes, this is a very strange (debatable) decision. One thing is generally available counterspell or occultism, another is necromancy. I think the roots lie in Human-Undead heroes like Ornella/Markel.