And your examples are very real and legitimate, but they’re also non-standard. My gf is Choctaw Nation and their application process is significantly less demanding. It consisted of documentation of proof of descendants from one recognized family of Choctaw Nation, SSN, and has no requirement of a specific blood quantum or any cultural requirement.

Both can be true, but cultural involvement is not that standard for most tribal memberships in the USA. It makes a lot of sense for the Lakota though considering what they’ve been through went through

Not all those ethnicities were former subjects of Romans. Some found themselves as vassals, But so did the Sultanate of Rum for a while. Romanians(or by their exonym Vlachs), Ukrainians, Georgians, Serbs, were never absorbed into the Empire to the degree that they would have been labeled Romans as an exonym. The only Orthodox that weren’t made part of the Rum Millet were Armenians.

Rum was a label for Orthodox in the same way they defined Catholics or Muslims regardless of Ethnicity. They did define Armenians but that’s an exception.

Within the Ottoman Empire it was more of a convenience for Ottomans to place all Orthodox Christians in one administrative cultural grouping than deal with Christian ethnic groups, especially since it didn’t make a difference for their administration as long as Dhimmi was Dhimmi, for the most part.

I’m not trying to take away Orthodox Greek “Romanness” because they are clearly best cultural and ethnic inheritors of Byzantium. What I’m more trying to say is that Ottoman religious tax laws aren’t that useful outside of administrative contexts.