Wet leather is abrasive??? Wet veg-tan is slick. It is typically tanned with oak bark tannins. You may be thinking of chrome tanned leather, which is unsuitable for a holster. It is also usually finished with resolene acrylic finish, so it really shouldn't be absorbing much water, if any.
I agree 100% about having a T-shirt between you and your holster.
Wet leather was always abrasive to me when it was moving against bare skin. Rough out or not. It was never "slick" nor did it just slide across my skin, like wet kydex does.
I dont know what they tanned the leather with, but I do know that some holsters "burned" more than others when against my skin that had been rubbed raw from the holster. That just added insult to injury. I didnt buy cheap leather holsters either. All were known, brand name holsters and the average price at the time was around $75 ea.
Ive tried pretty much anything you can think of to stop sweat from penetrating my leather holsters, and with no success. I work outside, year-round, in a physically active job, and temps here in the summer are in the upper 90's with high humidity. We're usually soaking wet on days like today by 9am, and usually stay that way the rest of the day.
This was the last Royal Guard I was using prior to switching to kydex. At this point, it was about a month old when I stopped using it. It sat in a "holster box" for a number of years before I took this pic and got rid of it. The duct tape on the back was just another feeble and futile attempt at slowing the sweat down.
The blued Colt Commander that rode in it, and the second RG I had and rotated with it on a daily basis, didnt last the summer before it was rusted to the point it had to have the rust/pits stoned out and was hard chromed.