When I was cycling with my old Roadie club some days we would average 24mph over a fair distance. Bearing in mind your taking your turn on the front in a rotation system and your less than a wheel apart this was easy to do (with concentration), and some days faster.
Even on my mountain bike on a good day, I could do 17mph over 10 miles, flat route and 29er.
Taking full responsibility for my own actions. I see no reason why doing a reasonable speed, and even over 20mph, providing the conditions are safe is an issue. Yes, due to assist it's illegal on roads, but there are many other factors, are you being safe, did you have assist on at time, wind conditions, are you going down hill etc etc.
Look, in reality unless your in Richmond park, London (we all know about the strava / roadie circuits) doing 40mph, hand off bars and drinking beer you are unlikely to raise an eyebrow with police etc. In fact, one of my friends is a very lucky police officer on a police mountain bike and I often stop for a chat along the county lanes to take the mickey. He told me unless I was being a total idiot e-bike or not, he wouldn't bat an eyelid.
Have we seen the figures on crime, using phone when driving, less police officers and prisons full. I think they have enough on their plate already!.