roman empire looking organization that is unaccountably the abolitionist faction in morrowind

It does have the tenuous justification in that the Empire's civic cult was literally founded by an abolitionist revolutionary movement, although in practical terms one would imagine that would have been weakened into tolerating first serfdom, then indentured servitude, and then full-fledged chattel slavery again. Though thinking about it, I believe it's gone back and forth on the issue over the millennia so it's probably more just the abolitionist bloc being on top at that time.

although im way more generous in that i think the toothlessness of critique makes it a bit more like Chinese dynasties (complete with multiple iterations). like noone denies the Ming were an empire but they weren’t terribly extractionist because there wasn’t much periphery to exploit.

That sort of fits the closest, doesn't it? A distant central bureaucratic hierarchy on top of otherwise autarkic regions that have only a tenuous connection to it apart from taxes and the provision of soldiers. That's more or less how I've seen Chinese marxists describe the state of things under the various imperial Chinese dynasties, at least (also literally where I first saw the word "autarky" ever was in a description of historical China from Chinese marxists).

besides the Orismer and Reachmen i cant think of imperial periphery

Black Marsh, Elweyr, and Valenwood fit the bill the best, I think. I get a definite sense that they're being subjugated and extracted from, although Valenwood is arguable there.

its very strange that the setting has 1 political center

I mean there are regional capitals and the regions themselves are pretty autarkic and more or less autonomous. The Imperial City is important for geographical and symbolic reasons, but in practical terms is distant and unimportant.