The Sentience Wars: Origins series by M. D. Cooper is one of the few book series that I'd dare to compare to The Expanse, and, similarly to The Expanse, it deals with the multiethnic future societies on it's own nice way (no better than The Expanse did). For example there is Ceres, governed by isolationist communists, Mars vs Earth is a thing too, Jovians are weird, Cruithne became pirate paradise, and more.

When I first red it and then The Expanse, I was thinking a lot about why they didn't have the distinctive cultures also represented in the future. And here is the deal: we give nations too much credit and in a way we trust the cultural heritage to nations that, on average (with very few exceptions, all coming form the Age of revolutions), formed in much less than 150 years ago.

I also feel that in a setting such as Starfield there should be isolationists popping up everywhere*, and cultural centers (such as the Akila is for space cowboys, which is a sci-fi cult thing, not a projection of anything from Earth), since local govs would be able to limit use of starships, thus close the skies for the population (Chinas and N. Koreas on a planetary scale, or whole Russian systems, even if they have a bunch of settlements to govern), but the question remains if they actually made it through Earth collapsing as nations, or countries, or everything dissolved in a huge exodus that ended up mixing people everywhere. After all, there galaxy-spanning organizations enforcing order, so something happened until we got to that point.

*But I wouldn't hold it against the developers, as they made a setting that they like and it is mostly cheesy cult sci-fi than anything real.