I hate it so much when people say that having a Pantheon is illogical for Chaos because it's Chaos. Have you ever heard of Warhammer 40k and Chaos Gods? Nothing prevents the existence of the Chaos Pantheon, which will fight each other for power and have little interest in other forces (which would explain why they did not interfere with Sargeras). By your logic, it doesn't make sense that even before Sargeras, the pit lords commanded their own armies because that's ORDER and HIERARCHY.