I can't speak for
@PM Cycles but it's pretty easy to see how having local jurisdictions legislate based on PfB's two separate classes (20mph PAS/no throttle vs 20mph PAS/with throttle) is a large financial benefit for Bosch (using Bosch as the catch all for Bosch, Shimano, Yamaha, Brose, and the bike manufacturers that use said motors) et al).
I think PfB's advocacy of 3 classes is cumbersome. Why have a distinction between class 1 and class 3, for example?
Under pedal assist pick a top speed and that's it. Many adults can maintain a sustained speed of over 20mph (sustained defined as 1.6 km or 1 mile flat), so why the artificial limit? MAYBE 28mph is too fast, but 20mph is certainly strikes me as too slow for some.
Maybe have a second class if a (speed limited) throttle is introduced, even if the throttle's max speed is slower than the PAS system, as there is a real, tangible difference between the feeling of riding under throttle, and riding under your own power, even if assisted by a motor. I don't think anyone would argue that.