I had an RTA twenty years ago. Some dickhead drove into the back of my bicycle at 70 km an hour. My cycle-helmet shattered his windshield and protected me from a serious head injury by its self-destructing makeup, the hard outer shell fixed to a polystyrene inner shell dissipates all the force of the impact. How is a pedestrian collision any different, except that the forces involved are much, much smaller. (500kg x 70kmph - *63kg x 20 kmph) compared to (85kg x 24kmph + 118kg x 14 kmph)
As was pointed out by your good self, one can be concussed without being knocked unconscious, it isn't entirely clear if the reverse is possible. I rather wear a helmet and not have my skull cracked open, than have my skull cracked open by not wearing one.
People only hear (read) what they want to hear (read), i already pointed out that solid helmets transmit the outside forces. To reduce impacts and risk of concussion Americian football helmets would have to break on impact, and be replace each time the outer shell was damaged. Otherwise they don't dissipate the forces involved.