So you have no photographs to show what you are referring to? Plus what unsolicited cleaning advice are you referring to?
For what it is worth, have a number of Rice barrels that I regularly shoot. Service and responses have been quick and professional when requested. My barrels. No observed or noted erosion. Now I have seen crud rings in multiple manufacturers’ barrels, but erosion has not been a problem in any of them. I don’t shoot as much as some. Probably burn only 30 pounds or so of blackpowder each of the past few years. With my limited number of shots, have found crud ring to be result of load combinations (projectile, powder, charge, lubricants and bore finish for example). Yet to see bore erosion in a blackpowder muzzleloader. Now with my smokeless Milsurp guns I have bore gauges and use a borescope. Bore erosion in those guns is obvious. But not a topic for this forum.