If the hero is a Dark Mage, then he acts as support for the troops, and the outcome of the battle is still decided by them. I would still recommend leveling up leadership with a speed aura + in combination with the "attack" skill, a really cool ability is unlocked.
1) Logistics - by default
2) Chaos Magic - otherwise, what's the point of racial abilities?
3),4) Leadership, luck - according to recommendations
There is one empty cell left - so you have to choose between attack and dark magic....
And a mage without spellcasting...:rolleyes: