Given the apparently-terrible injury-to-death ratio, another angle to attack the legality of the action might be that the weapons were first and foremost effective at maiming, not killing, which is generally frowned upon by the laws of war (if they were intended as lethal, their success on that front was so bad it might fall into "guilty through incompetence" sort of territory)

(I agree the targeting per se seems to have been remarkably good for the world of asynchronous warfare—or even conventional warfare)