We just need ROF rules plain and simple. My suggestion if people want a bb hose they need to give up fps. So figure out a rof limit that if people go over it they need to drop the FPS to something like 300 or 350 and under, then make a hard cap on much ROF any replica can shoot.
Now that aside one thing that urks me is this idea that P* guns hit harder, which make 0 sense for a single shot. If it leaves the barrel at X fps that's it. "but heavier bbs" yeah and AEG's can and do use heavy weight bbs joule creep is a real thing but it is not exclusive to P* guns.
My best guess for why people see to think they hit harder are one of 2 idea's and both include the ROF so ROF rules would fix it.
#1 The high ROF+high accuracy makes multiple bbs hit in the same area or even the same spot almost the same time hurting a lot more.
#2 The high ROF lets bbs follow in the low air pressure made by the bbs ahead of them, reducing drag those increasing persistent fps making them hit harder when they impact.
It also could be a combo of both but again good ROF rules would fix this and singling out P* guns alone would only push the people that like to abuse the high rof to invest in high end AEGs and with these new godlike mosfets, brushless motors ect they can get insane ROF without being weighted down by a tank, regulator and hose.