I’m not entirely clear how your posted images were generated.
It has been my experience that exporting a 100% JPEG from a NEF or TIFF does not significantly affect fine detail even after 10 consecutive imports and re-exports. Where the image does degrade on successive saves to 100% JPEG is in posterization of solid colors.
This shows up on my website under Button 10 at the bottom of the page. Click on Item 1 and look at slides 7,8,9 in full screen mode.
It’s a moot point. I certainly would not recommend use of the JPEG format for anything other than exporting images.