My experience with Kydex and Kydex-type rigid holsters is that clean plastic rarely causes any short-term damage to the finish itself; it's the grit or dirt/sand/metal shavings, etc., that very easily get embedded in the Kydex that does the serious damage. Most plastic holsters will leave a streak of plastic on parts of the pistol, but the plastic itself just isn't hard enough to scratch through the finish in just a few draws without "help" in the form of something on the pistol or in the holster. Sometimes folks have thought a pistol was scratched, only to clean it up with solvent and find that the metal streak they saw was actually a streak of soft aluminum on the outside of the pistol's finish, and it went away when the pistol was cleaned.
Lined holsters will help prevent or spread-out the extreme pressure-points of more rigid holster designs, reducing wear, but they will NOT prevent the same type of damage if grit/dirt/metal shavings find their way into the holster lining. And once the lining of a lined holster is contaminated, it's very difficult to find and clean the debris out to stop future damage, unlike plain Kydex/plastic.
When I shoot outdoor matches in windy North Dakota, my holsters rapidly get coated with dirt/grit, inside and out. It can be very hard on a pistol's finish. I always tell folks if they want to keep a pistol looking pristine, then they shouldn't even BUY a holster for it, let alone carry it or draw it from a holster. Or buy two pistols of the same model; one to use, and one to gently wipe down and display on the padded shelf in the safe.
