yes… they don’t do much towards stopping the brain rattling around inside the skull.this can happen in any collision but the severity/risks go up if the head is directly involved in the collision. hence the need to also reduce conntact sessions in training.
(you would need something like some of the cycling helmets that give more dampenning. i’ve had a couple of nasty crashes on my bike and i can vouch that they work! in both cases the helmet was trashed but, when examined, was told i didn’t have any concussion symptoms, downside they tend to be a bit bulkier - not to be the best fashion statement , and they are single incident only. one high tech helmet is a coller that has sensors so it can detect a ‘bad’ collision and inflate the collar to surround the head - could be entertaining seeing two props collide then suddenly their heads disappear )