You raised some excellent points with your observations. For me anyway, the action looks "right" with the placement of the joints with the 4 sections. This is going by what I can recall from seeing many suckers swimming over a lifetime. Of course the action is probably somewhat exaggerated compared to the real thing.
You mentioned how different fish swim compared to one another which is a great point. I have noted that making the shape of the lure as close to the actual fish you are simulating does automatically get you closer to what is correct.
The panfish profiles such as a bluegill or crappie tend to have a very darting and tighter swim compared to a cylindrical fish shape such as a perch or walleye.
I think that there are many factors that come into play when trying to really get as close to a live fish motion and the placement and spacing of the joints is probably the most crucial after the body profile.
Regarding weight placement I've found it not to be a major factor as long as it is low enough in the belly to give stability. I do tend to avoid weighting the very last section by the tail although prototypes still swam well if I did.
Well, I'd better get back to airbrushing now but thanks for raising some great points.