Track rotation will be informed by the people you are racing against. As I understand it, the track selection is capped with respect to the lowest-ranked player. It'll try and match-make you against similar ranked people, but if that is not possible, a wider net is cast. So if you race against people of similar rank, you'll get track options in line with that. But if there aren't enough people for that, you'll have lower ranked player pulled in, and thus have lower tier tracks available. For my part, I've absolutely had races on hard tracks, but have *mostly* seen the lower-tiered tracks due to capping. The MP isn't feeling like it is thriving. If it was thriving, I'd expect to be mostly racing tracks in line with my rank, but that isn't happening much.
RL posted an FAQ that clarifies the MP rating system, and how the track selection works:
https://forums.ubi.com/showthread.php/2021555-Season-1-FAQ-Tracklists
I said previously it was 'ELO-like', but it is apparently the following, specifically:
https://en.wikipedia.org/wiki/Glicko_rating_system
Now, on reading that, I think it makes sense. But *MAN* they've not done themselves any favours by not tutorialising nor explaining the ranking system *in game*. People see confusing hard swings in their score that *seemingly* make no sense. And even when you *know* the why of it, it doesn't feel great. Edit: Also, it almost feels like there are two systems, not one. The per-heat scoring (10,8,6,5, etc) bears no relation to the glicko rating, but it is what people *see* when racing.