Yesterday, I played Tower versus Necropolis on a large map:
The combination mentioned above is deadly for everyone! The hero is constantly on the move, and there's plenty of mana thanks to artifacts and education. BUT! It requires high levels; it won't work on a small map.
The Necropolis suffered terribly without Dark Energy, but the arrival of high-tier units still caused significant damage!
With this combination, victory is guaranteed!

Didn't the Necropolis have anything to counter your Chaos army? It has several options... for example: Reflection, Undead Protection against Chaos, Magic Drain. And if it gets lucky and takes Magic Resistance? Plus, the Deadly Misfortune effect when Daedra screams significantly reduces the chance of your lucky spellcaster's ability to trigger. IMO, Chaos is less effective against a skilled Necropolis player than summoning.

Added 4 minutes later
In general, mentoring is very effective on large maps. Before the main battle, thinning out the enemy army with low-tier heroes leveled up in Chaos is very effective + it's also very demoralizing!