Chaos magic. Is it necessary?

Of course, chaos is necessary. Firstly, it provides the player with a wider range of tactical choices in battle. The more possible combat approaches, the more interesting it becomes. Secondly, other types of magic are more effective in prolonged battles; you cast a spell once and reap the benefits throughout the fight (of course, if you're a mage). But in smaller skirmishes, where it's possible to win without losses and quickly, chaos is the ideal choice. Thirdly, a warrior will continue to deal damage until they are killed, and it's inefficient to expend the attack power of a large unit on the remnants of a single unit; that's where chaos comes into play.