I perceive eBikes as an opportunity for younger people who don't cycle to get more involved and be satisfied the parameters are high enough for them to want to.
20mph is exactly the figure I had in mind as being sensible as a limit. I won't comment on the throttle issue because I don't think it actually makes a difference - a bike going at 20mph on a pavement or footpath is a hazard and I would never cycle like that. But I could easily do so on a push-bike if I wanted to. So again I don't see that this has any relevance to the power-assist limit. If there's a worry over speeds on cycle paths then put a speed limit on them.
Limiting the bikes themselves is a lazy way of trying to enforce an unwritten concept which cannot work in practice as they can be ridden over that speed if people want to without assistance.
I can and do understand your arguments for a higher assist speed, but as you've shown, it can bring about demands for more regulation or usage exclusions just as has happened elsewhere. Those separate the e-bike from a bicycle so are undesirable for that reason alone.
The 15 mph assist limit law as it stands reflects the majority range of cycling ability, so it makes usage exceptions and added bureaucracy unnecessary and administration easy. In other words, it gives all of us almost complete and very desirable freedom. Higher speeds are not suitable for shared footpaths, many cyclepaths and bridleways and other places where animals are found unleashed and under limited control.
Limiting the bikes isn't a lazy legislative concept, it's to expressly take care of the fact that cyclists are not tested for competence in the way all motor vehicle operators are. The average human when at their fittest can run at up to about 18 mph and evolution over the millenniums has equipped us with the commensurate reactions and eyesight. As I've described before, this is self-adjusting, our abilities deteriorate in synchronism with age and infirmity, the elderly with poorer eyesight and slowed reactions can no longer run at 18 mph.
So we are self testing, the cyclist who consistently pedals at 20 mph unassisted is naturally safe at that speed due to their inherent fitness and relative youth. Someone power assisted at that speed is not self tested, they could be dangerous without anyone knowing it, least of all themselves, since everyone rates themselves as above average, an impossibility!
So an assist speed limit has to be integrated into the e-bike when the rider is not tested for proficiency, just the point at which that is set being in contention. You feel that it should be 20 mph, we've had others arguing for 25 mph, while many feel 15 mph is fine. The authorities worldwide have or are currently largely settled on 15 mph being appropriate. It is a widespread common natural limit of normal cycling speed, most of the world's cycling done at or below that, so no special control measures are needed.
That is not true of 20 mph, that being the province of the lycras and some commuters in a very few places, almost invariably with drop handlebars when on unpowered bikes, emphasizing the sporting nature of such riding. They are, as described, naturally self tested for suitability.
So I'm a strong supporter of the simplicity of a law that gives near total freedom without the petty restrictions of routes I can't use, compulsory insurance, registration, helmet wearing and number plates. Those things have all happened elsewhere when higher speeds have been allowed. As things stand we already have a large proportion of our population hating cyclists and calling for taxation and more regulation of them. Power propelling ever larger numbers at higher speeds would just ensure they got their way to our great disadvantage, since our legislators are always happy to restrict our freedoms. It's what they do and their purpose in life!
Lets just count our blessings and enjoy the almost unique freedom that we have, shared only by those other pests, the pedestrians!
.