There is no fight to referee here. If chaos and legion is both just paradigms, ways a mind organize belief, then asking who win is like asking does addition beat subtraction, it don't make sense cuz neither one is an agent with fists to swing. You gave legion and chaos a body and a will they don't have, that's the mistake, you turned a method into a soldier.
And notice this question just bring back the same dualism I already tore apart in the last post. I said opposites ain't really rivals locked in eternal balance, charge ain't hot fighting cold, matter and antimatter just annihilate not "battle" each other. So why now you asking who wins between chaos and order like they two armies on a field?
Also "win" is not defined so the question is empty. Win means produce better result, win means last longer, win means dominate the other paradigm in your head? You never say, so whatever answer someone give you they just picking the definition that make their side win, that's not logic that's just choosing the outcome first then backfilling the reason.
And the setup itself already assume the answer: you say legion is "gathered and assembled according to rule" like that automatically make it stronger, but that's the exact thing you supposed to prove not something you get to assume for free. That's circular, you asking a question that already contain its own conclusion hidden inside.
Last thing, you mixing three different "chaos" and calling it one word. Chaos as a magickal paradigm (belief based, psychological), chaos as cosmic primordial state, and legion as a specific mythic entity, these ain't the same register, so the question is really three questions wearing one costume, no wonder it got no clean answer.
Real answer if you strip the fallacy: nothing win cuz nothing is fighting. Structure and non-structure is just two lenses a practitioner pick up depending on what they trying to do, one lens don't beat the other, you just put one down and pick up the other one when it useful.