I think Good Soldier Schweik is saying that Mance's version is better than Mark's just because! Because Mance is old and black and authentic, man!
Well, Mark was young and white and - I bet - spent a lot more time perfecting his art than Mance.
To my ears, every element of Mark's version is better than Mance's.
We can admire these old "authentic" performers, but don't try to tell me Mance was great in any way. He was interesting in that he gave us an insight in to a certain musical past, but Mance, himself, wasn't a great artist.