I would like to agree with your theory, but at times I'm partnered up with people who have huge differences for my score. But maybe that's just because they didn't FC the song. Ah oh well. As long as I get an average of 1k-1.1k points every 5 playings, I'm fine with this whole thing.
Played this game since around May and still no UR for me at all. Would be nice to have one for the stats and possibly the skills, but I'm starting to think that it's ok if I don't end up getting a UR anytime soon.