I dont think he is correct, that pipe is essentially doing just that, dumping off exhaust to control your boost level.... If you have the pipe with the deltagate the reroutes the expent gas back into the downpipe, its doing just that, vent to atmosphere via the downpipe so its QUIET and should control your boost rock solid...
My green car has the external pipe with a gate from atr, my boost is rock solid, if not then you might try lubing your valve... if the valve sticks open it will slow your spool and your boost will fluctuate because the valve isnt moving correctly....
Do you drive the car often?
BW