alt Hacker NewsWattage is basically meaningless. There is nk standard way to measure it. Almost all "250 watt" ebikes consume much more than 250 watts of electricity at full throttle, and can produce much more than 250 watts of mechanical output for seconds or minutes at a time.
The fact they listed wattage and actual peak wattage is different doesn't change the fact that an e-bike's power, not whether the throttle is connected to the handle bars or the pedal, is what actually creates fast and dangerous bikes.
If regulation based on power was drafted, it'd be a simple matter of using a voltmeter and galvanometer to see if a bike is compliant with power limits (arguably motors have different efficiencies, but electric motors are close enough to 100% to use this method).