All of those shots you linked to are effects/composite shots, which are going to be softer and grainier just by the nature of how they were done (multiple layers of film layered on top of one another). 4K83 in particular has shown (to me, at least) that ROTJ’s effects shots are noticeably less sharp/defined compared to its “pure”/non-composite shots.

Some of those shots might have been “Despecialized” using low resolution laserdisc/GOUT material, too, since they may have been made before higher quality sources like 4K77 became available. I’m not sure about that, though, and I don’t know which version of the AVCHDs you have (2.0, 2.5, 2.7), nor do I know offhand which GOUT shots remain in which versions.