Earlier quoted context omitted.
Motorcycle>bicycle>skateboard. There is simply more inertial mass on a Moto, which allows you do use the front brake to its full potentail without pitching a faceplant. That and the suspension absorbs some energy. Also, the rider position is usually COG to the rear. On a bike, your body position on drop bars puts you more COG forward, steeper head angle, more levered over the front friction patch (tire/road). The bik…
I think the problem here is that people are conflating an enforced stop - hitting a rock - with a normal braking stop, and even then with an emergency stop. If the issue is - is an electric skateboard more dangerous than a bike? well, then of course it is. You're less visible, less stable, and have less braking ability and much smaller wheels. But that's not to say you can't safely brake a skateboard without throwing…
With regards to breaking when you don't have a rock, curb, door in your face...You can program anti-lock braking into an electronically controlled breaking system. If you have enough understanding of the friction of the rider to the board and the boarder is experienced enough to know how position themselves during braking, that system should win as it can avoid skidding. Regarding experience level: on a bike it takes some experience not to just use the front brake only and drop your head on the pavement.
Until we see some stats about which group actually sustains more serious injuries, commuter bicyclists or commuter boosted boarders, the jury is still out.