Eureka!
So, like, I made some blah blah blah posts about 仙舟 being a homophone for 先周 and something something 六军 stuff.
But but but! There's another more obvious homophone I wasn't thinking of and only just recently thought about because I was listening to some old songs and got reminded.
So, in Chinese, 神州 (Shen Zhou) is the shorthand for 赤县神州 (sourced 《史记·孟子荀卿列传》). 赤县神州 is the ye olden name for the political entity know as 中国 (Middle Kingdom). (Technically not China due to complicated political definitions across historical eras, but also is China.) Later, 神州 became the poetic name referring to 汉地九州 (Han Di Jiu Zhou). 汉地九州 refers to the, uh, Han dynasty's territory of nine provinces (冀州、豫州、兖州、青州、徐州、扬州、荆州、梁州、雍州). (Yes, that one's literal.)
Now, the character 神 (shen) is often compounded together with the character 仙 (xian) to make the compound phrase 神仙 (which can refer to either gods or god-like immortals). What I'm trying to say here is that 神 and 仙 has a very strong association. (Although they do in fact mean different things; 神 is god while 仙 is immortal, and the two groups of divine people have very different cosmic bureaucratic responsibilities.)
Sooooo, if we replaced 神 with its commonly associated 仙 and 州 with the homophone 舟, then we effectively turn 神州 into 仙舟. And and and, the Xianzhou fleet had nine ships initially. Guess what 神州 has? Nine 州 (provinces). (Chinese language does not have plurals. So yeah, the singular and plural is context dependent and interchangeable.) So.
What am I saying? Well, I feel like it's reasonable to conceptualize each ship in the Xianzhou fleet as a "州" (province) in terms of its political reach. Like, I get that canon says technically these ships are the size of planets, but at the same time, the political system is more like a provincial government than a country level government. At least scale-wise.
Of course, this doesn't change the fact that there's still this complication that the transportation carrying 天将 (Arbiter-Generals) from each ship is also called 使节舰, a diplomatic envoy, which implies that these 天将 are more similar to being an ambassador/emissary. That suggests the governance on these ships have a certain level of autonomy. Yet at the same time, there's apparently some kind of higher-up/hidden political body that can apply political pressure on the Marshal...
There's essentially no real consistency to the political structure and either interpretation ("each ship is a province" or "each ship is a state") is completely reasonable.
Not sure how to end this blathering, so I'll just stop.