The stuff I like the most is stuff I can treat like crap...Whatever, Dr Jones. The fact remains that leather only fails like you've described if it's constantly abused and treated like crap. All the stuff that you've described has to be on a daily basis for any of your arguments to be valid. Otherwise, the worst you wind up with is a slightly scuffed-up holster. But whatever, Adventureman.
Around my place, leather left for a couple months, even in closed containers, invariably molds... I've never had a kydex or polymer holster mold or crush.
Leather holsters are prettier...