The physcology of the rider is very important, these laws are constructed to cover all skills, competence, age and perceptions of danger humans have.
Being able to sustain 20mph with zero effort is completely different to having to work for it, the brain quickly accepts the new parameters as the norm.
There is no apparatus to mentally slow down ebikers as they transfer from open road to cycling through pedestrians, add in the factor of the perception they are riding a harmless pushbike and the silence of an ebike increase the potential for collision.
Im sure every possible outcome with data to back it up was endlessly debated with activists and pressure groups on both sides.
I would love more the 15.5mph on my emtb in Europe, but that means everyone gets it, including seniors with dodgy balance and teenagers with little development of risk.
This bill hasnt followed a tiny part of that path towards a balanced conclusion, its reactionary grandstanding by an institutionalised class who are running with..if you dont play nice , then no ones having it.
With regards to gravity assist, I dont have any info on wether roads and signage are designed to deal with the extra potential for speed, going fast downhill and developing the awareness is a skill developed since the wheel was invented, its a shared experience for everyone and the spectacle of a fast descending rider generates a group awareness that ebiking has yet trigger.
The elephant in the room is the extensive import and modification of illegal motorcycles, ee are all sat here thinking when is this going to be banned , it appears to be hanging by a thread off the back of net zero.