Here we go down the rabbit hole of definitions.
As I understand it the 250w rating of motors is what that motor can take continuously without overheating.
So, a motor that can run at 800w that doesn't hot complies with this 250w rating. Then, if stamped by the manufacturer as 250w, it is legal.

This is what makes the nominal power definition bonkers - as far as i can see, it's meaningless.
It is power that does the work. Would a more precise way be to limit the power output of contollers? Not current as a 10A controller at 36v outputs less power than a 10A at 48v.
However, if controllers were limited to an output of 250w, given inefficiencies in the system, I certainly would no longer be cycling the hills of west Wales.
I do agree about Bosch though. I wouldn't go near their locked in products.