Chaos magic is worth taking if they persistently prevent you from using Light magic. Or as an additional option... to first buff your army with spells and then indulge in Chaos magic. You'll get the most out of Chaos if you max out the Elf's racial abilities: Rain, Enchanted Arrow, and Avenger. Enchant the arrow and blast the enemy with spells. Even with a small spell power for the Elf (relying on artifacts and map objects that give a bonus to spell power), the damage will be tripled (3 cursed enemies... 3 arrows... 3 spells at once), and it looks cool. But Light magic is still more useful for the Elf.