Video really shows what a total non-threat the 250w pedelec is on mtb trails. A mod to one of those bikes only increases top speed. Does not effect power below the limit at all.
It's really contorted logic to say: oh, well they could have a BIG engine. Sure, you can rip off your smog control on your car too. Then it's illegal.
Let those who do use the 250w yamaha or boshe properly on trails where they are in effect just another mtb bike which can climb a bit faster.