Any holster is going to show wear over time, but I would probably disagree with your smith.
A properly made Kydex holster will probably have less wear on you gun. A leather holster will, over time, collect grit on the inside of the holster. This grit will wear on your gun. The kydex holster can just be wiped clean. The MTAC is different because it has both materials, but has the smooth side of the leather toward your gun.
If this is a carry gun, IMHO, wear shows use and that is not a bad thing.