On small maps, Chaos has some advantages in terms of magic. A single Lightning spell can take out a lot of units, including heroes. But if you consider large armies led by a hero-mage, maxed out in magic skills, Chaos is not in the best position. Even Disintegration, dealing 2000 damage, won't significantly harm the army. One of the undeniable advantages of Chaos at high levels is not combat-related – it's the Confusion Cloud spell. Cat reflexes and overall first strike are also very good. This is an undeniable advantage for Chaos mages.