Yeah, the SW mono mix as far as I remember is mainly based off an old VHS recording from a European tv broadcast in the 1980s, and the Story of Star Wars LP record from the late 1970s. The completed reconstruction sounds listenable, but it's basically a 1980s VHS recording in terms of quality, so this should explain a lot about why it lacks bass, sounds muffled and has poor dynamic range. It had a lot of noise clean-up too, which may have taken some of the edge off of it in other respects. It would be unfair to expect it to compete with a new, professionally ripped mix.

One way to appreciate what good mono would sound like is to simply listen to a good stereo mix in mono; most receivers have the options of "monoizing" any sound input so as to fold both channels into a single one and then play it back from the left and right speakers. The mixing levels might not be right, but the sound quality in terms of its crispness and bass might give you an indication. In theory, a mono mix, a stereo mix, and a 5.1 mix all made today would be 100% identical in quality, just utilizing more directional effects depending on the format. Of couse, most if not all mono mixes are from the 1980s and earlier, and so the recording quality of the master is not as good as today, so they won't be able to completely compete with a new mix in whatever the format is. But, properly presented, the sound quality should be good.