I have a class 3 ebike. The only difference between it and a normal bike is that I don’t have to work as hard to turn the pedals. As a result, I can go up hills easier. And maybe go a couple mph faster than my body would be capable of on a normal bike. But the overall experience is the same as biking. I’m still burning some calories, and going up hills isn’t exactly easy either. It’s a fantastic balance which turns biking from less of a sport and exercise into more of a fun activity.
I’m not regularly going anywhere close to 28mph either unless I’m going downhill. It’s very comfortable to pedal at 15mph or so. (E.g. the ebike doesn’t make me feel like I must go fast all the time.)
Once you step outside of this class-based system, I’m guessing the law changes pretty drastically. An electric motor on a bike allowing 50mph speeds is probably not treated by law as a bicycle.