I agree with that statement. An RS500 T4 has a wastegate penny covering a hole of about 20mm and even when it's been ported for big boost it can't be more than 25mm yet that handles 500+ bhp.

I use a little 38mm gate on my turbo rated at around 400bhp and even finite little adjustments in duty change the boost characteristics dramatically. It has to be done carefully to get and maintain correct boost levels