From what I can determine, lead actually reacts in it's passage through a bore more like lubricant than a cutting agent and when lube is added it is even less prone to barrel wear.
Linen (cotton) cloth patching has the effect of smoothing a bore of reaming and rifling abrasions. Paper patching is more abrasive but will work for many thousandsof rounds before accuracy suffers.
It was said in the chunk gun era that target rifles would shoot smooth, meaning the rifling was still sharp but a glaze would form and accuracy would suffer. The remedy was to clean with some vinegar and let stand a bit to rough up the polish or glaze that had formed. My guess is this may have been nothing more than carbon fouling which is often very hard to detect and even harder to remove.
Black powder pressure and temperature while combusting does not seem to erode rifling very much if any as can be seen in the breech area of muzzle loader or cartridge guns.
Having built and serviced many rifles and hand guns for a lot years I have concluded that lead bullets and black powder pressure simply do not wear out barrels but rather loading, wiping between shots and cleaning procedures are the real cause.