I agree with others that barbel degeneration (wearing away) can be due to sharp substrate material or bacterial issues or both. The gravel in the photos in post #3 does not appear to be rough, agreed. But it is not the best substrate material for cories.
With one exception that Ian Fuller pointed out to me (and which I cannot now remember), all species of cory live over substrates of either mud or sand. They naturally sift through these mud/sand substrates, in the process of which they take up a mouthful of substrate, extract any bits of food, and expel the sand/mud via the gills. You cannot do that with large gravel.
Another issue with gravel is that bits of food take longer to decompose than in sand, and this can sometimes lead to bacterial issues. I have seen barbel degeneration on cories over pea gravel, and I suspect it is likely the bacterial issue more than the roughness.
I had cories over small gravel for years before Heiko Bleher convinced me that it was not good. Nothing he said is better than sand, and since I changed to sand some five or six years ago, I would certainly agree with him. I can't really explain it, but there was a difference in the cories.