I think that there are extremes that need to be quantified here.
SBR shooters regularly clean right down to the metal to keep their rifles super accurate..
A guy who is looking for an accurate PRS rifle however , is not going to be so worried about a squeaky clean barrel.
My prone match guns don't get " decoppered " on regular basis, but they do get cleaned of copper every so often if I expect to keep scoring well from 500 to 1K for 10 or 15 rounds per target .
However, my favorite hunting rifle has not been " decoppered" since it was built in 2009. it has however had a regular cleaning with Amzoil or Mercury Quicksilver Power Tune to get the carbon out, and some G96 pushed through it.
I firmly believe that carbon build up in the chamber area of a rifle hurts accuracy far worse than copper from 200 rounds of match ammo.
Many years ago a champion silhouette shooter showed me his PH 1200 270 Winchester hunting gun, it looked like the barrel was painted with copper!
It had a total of two shots through it, and was sparkling clean before those two shots. He told me it would look the same after 100, and the accuracy would still be excellent.
Cat