There has been much debate on this topic the last few years. The fact is both kydex and leather will wear a guns finish. The consensus is that kydex will wear at the retention/contact areas and once the gun wears the edges off in those areas the wear stops unless the holster is dirty. Unlike leather, kydex doesn't maintain full contact with the firearm so any finish wear will be limited to just the contact areas and only during break in. Leather on the other hand maintains full contact with the firearm for its primary retention. That leather attracts and holds moisture, oils, sand, grit, and powder. Even though it may feel soft the abrasives are present and those abrasives will consistently wear the metal even after the finish is gone. Guns carried daily in leather have a distinct look to their finish seat especially if their blued....or used to be. I personally think guns with leather wear have a lot of character.
I make a habit of periodocally rinsing/wiping out the inside of my kydex holsters because those same abrasives collect on the inside of them as well but the big difference is that they can be easily cleaned out unlike leather where they get embedded in the leather.
I make a habit of periodocally rinsing/wiping out the inside of my kydex holsters because those same abrasives collect on the inside of them as well but the big difference is that they can be easily cleaned out unlike leather where they get embedded in the leather.