The lack of Chinese people on Firefly was a bit of odd. But I gather Simon and River Tam were to be viewed as being from Chinese as well as Caucasian descent. And I think that the Chinese in the 'Verse did have their own planet, we just never got to see it. Did they become isolationist? We'll never know. The short run of Firefly did limit the back story so a lot of it is presumption and vague memories tweaked from writers' brains.

but there, yet again, the sole black male dies

And the sole married man dies as well. Joss will kill anyone to further the plot.