I would venture to say that in your situation there is probably restrictions in the valves in the PB piping system. When you remove the entire system you will probably not have any problems.
The plumber should be testing the water pressure @ the meter or where it enters the house to determine what your pressure is. Post back what your pressure is; 60 is normal, 80 is high. You could have high water pressure and not realize it since there are restrictions in the piping system.