No idea, I'm not an expert, but he uses CEDAR for noise reduction. The 5 JSP Fats Waller sets I have sound rather "dead" to my ears, though not as bad as the RCA sets that were issued in the 1990s.
Cedar is a suite of tools and each can be used to different degrees. Much too broad a stroke to complain about the system. He might deaden the sound before using Cedar. You never know unless you know what he's using and how. It is like blaming Studer for a lousy recording.
Since you edited to talk about the RCA sets, they were done over an 8 year span with different tranfer and mastering engineers. Some of the later sets sound wonderful. Once again, too broad a stroke.