If all other attributes equal, boxing will always be the most effective stand up art, because you can fire off shots immediately, going forward, backwards, side to side, don't need need space, can throw punvh conbinatuons faster than kicks.
It it turns chaotic, what usually always happens, 2 fighters start throwing hands. If you're both in awkward positions, or angles, pucnhes are easier to throw than a kick.
Less chance of getting checked, and injured, where serious, or a really bad stinger. Just much easier to implement a boxing game plan than any other art. Also, when someone throws a leg kickk, you can firee back faster than they can retract their leg.