Every holster wears your guns finsh, no matter what its made of.
If you wear your gun every day, and especially if you have an active lifestyle, you will likely come out a lot better in the long run, with the kydex holsters.
They dont suck up sweat and get, and stay soaking wet, they dont embed abrasives into the holster, just aggravating and accelerating the wear on the gun, and they can be easily cleaned under the kitchen tap, and dried with a paper towel, they dont rub you raw, when your shirt rides up and the holster ends up against your bear skin.
Yes, they do tend to wear your guns finish at specific contact points, but those are often small, and unnoticeable.
Leather, on the other hand, tends to wear the guns finish more overall, because it contacts more of the guns surface. Wet leather doesnt dry out overnight and isnt at all friendly to guns with rust-prone finishes, and even those that might resist it.
My rust issues went away as soon as I switched to kydex holsters.
And one big difference between the two is cost. The kydex holsters last/hold up to hard, daily use, basically forever, and usually at about half the price of a decent leather holster.