I have a three bk2's one in custom Leather one in an custom kydex and the 3rd in the original kydex like yours
I just checked all Three of mine I can't see any of them is any duller than the rest.
I mean if for some reason a guy draws and pushes the blade against the kydex really hard and draws it like that dozens of times a day it might possible dull it some,,,,,,,,, but with normal stright up draw I don't see it dulling it to any noticeable degree .