I think the only sensible part of electric assist bike law is the assist speed limit to keep them akin to bicycles.
The power available within that is a matter for designers, not legislators, and they should be free to provide a range of powers to cope with all hills for every degree of user fitness, enabling all the elderly and the partially disabled to be better served..
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The upper weight limit has no point and shouldn't exist since designers will always try to make e-bikes light anyway.
It's not just speed that needs to be limited but momentum and acceleration as well.
If you get rid of the power
and the weight limit then you could turn any powerful electric motorbike into an ebike by adding pedals and limiting it to 15mph, you could get some real two wheeled tanks.
I think that the power limit could in principle be replaced by an acceleration limit to allow for more power uphill etc., but I'm not sure how practical that would be. In that case the weight limit would need to stay to stop two wheeled monsters, but as you say it doesn't really effect most manufacturers who are trying to keep their bikes as light as possible.