Whilst this individual is clearly being a bit of a tit, riding so fast in and around slow moving cyclists and pedestrians, it's one less guy in a car hauling 1-3 tonnes of steel just to get to and from work or the shops. It seems a pity to me that we are not able to utilise >250W motors due to our backwards laws. eBikes have the potential to green our transport system, with our CO2 emission targets and Paris agreement, you would think we might have some joined up thinking and not have to contend with 15.5mph cut-outs whilst hybrids and inefficient eCars are rammed down our throats as the only solution. A fit rider can easily beat the limiter speeds on a road bike whilst on the flat. It seems grossly unfair that the majority of motorists are able to flaunt the rules of the road, and drive massively overpowered engines with ridiculous top speeds whilst endangering the lives of more vulnerable road users and carry on polluting without repercussion, whereas legislation prohibits the uptake of greener technologies.
Personally, I would have no qualms about defeating the limiters, or using powerful motor (>250W), but I would be discreet about it, and make a point not to endanger others. Disc brakes should be mandatory due to the higher velocity. The only problem is, if you are involved in an accident that's no fault of your own, the law might throw the book at you, and settlements might be reduced. You'll likely get points on your license too if you drive.
A point about defeating limiters vs using more powerful motors, the latter often makes more sense, because a more powerful motor would be able to haul you and goods at the limit of 15.5mph, whereas the 250W motors would be quite underpowered, and prone to overheat and become less efficient at travelling at higher speeds. That said, I understand why the motor is limited, because if we have idiots flying around on poorly maintained bikes with high power motors, unregistered, and no safety checks or third party liability, it's a recipe for disaster. I think more work needs to be done getting people out of polluting cars and on to sensible (but slightly faster than current legal) e-bikes to make them more attractive.