I also find some modern cars have the most powerful and blinding lights in general that it is tough to ignore the impact they make when passing. Some of the latest vehicles are totally blinding where as older vehicles seemed to be very consistent.

I was a firefighter for many years, and it used to be the practice at major incidents where multiple fire engines were deployed that one vehicle would be designated the "control point", its blue lights remaining on, and the others would turn theirs off. This was less about reducing the danger of dazzling other road users than about directing crews arriving at the incident to a place where they could receive their orders.

I suspect that nowadays the view is taken that if emergency vehicles turn up en masse and particularly if they are presenting a hazard to other vehicles by their positioning, they should all keep the lights on. Not just because it makes sense where there is no need to identify a particular vehicle, but because they're less likely to be prosecuted for not showing sufficient warning to other road users if there's a collision involving a stationary emergency vehicle.

As to whether the brightness of the lights can be mitigated, I'm no expert in vehicle lighting technology, but I guess they only have two options, which would be on or off.