You bring up a key factor here: mass. A traditional bicycle weighing 10kg, going 20kph has far less force/momentum than a 35kg ebike going the same speed, and when using the throttle, the acceleration rate from 0 to 20kph increases dramatically as well.

Currently in the US we have people riding class 3 ebikes (and particularly cargo bikes) that can have base weights of 70 or 80 lbs, plus the weight of the cargo, all going at 28mph with a throttle. That’s too much momentum to be safe around pedestrians and other bicyclists on multi-use trails.

IMO once ebikes start getting up to 750+ watt motors with a base weight of over 65 lbs, they should probably require some kind of licensing to operate, and perhaps insurance as well.