N.K. Jemisin takes a stab at the now tiring debate over whether epic fantasy in faux-European settings can include women and people of color without rewriting (imaginary) history. It's an interesting topic, as always, and, as always, Jemisin is brilliant in her response.
I don't have too much to add to this conversation, but I will say two things:
1) I was actually surprised that there were any people of color in Martin's world when I first started watching the show. I'd become so used to epic fantasy featuring no people of color (or "evil" stand-ins for them in the form of inhuman critters like orcs) that seeing an actual civilization of non-white folks in a world which is so very much Anglo-European for most of the show was a bit of a "well, isn't that unusual" moment.
That said, I recognize that Martin's world doesn't actually do much with this (based on what I've seen and read, mind). So the criticism of his treatment is valid.
2) I used to be one of those people who would say "but that's how it was back then" as a defense of epic fantasy. Then I went to college. And took some classes on colonialism. And British literature from Chaucer to the Victorian Era. And African lit. And Indian lit. And all these things. And it became very clear that this whole "Europe was white" thing was, well, bunk. It certainly was mostly white (based on my understanding), but even Shakespeare wrote plays with non-white people as part of the main cast (Othello and Titus Andronicus, for example -- the title character and a secondary character, respectively). In the early 1600s (maybe late 1500s). So, no, the excuse is bad. It comes from a position of ignorance, which we're all able to correct. And it's unnecessary. You can write fantasy set in faux European settings *and* include PoCs. Or you can try to write worlds with whatever the frick you want. It's fantasy, ffs. If you want to mix it up and have a story about Chinese-esque dragon riders, then write it.
In some sense, I think the confirmation bias endemic to epic fantasy's Euro-myths is one part ignorance and one part unwillingness to imagine. But it's also probably rooted in everything you've written up there, too. The thing I still don't get: why does this remain a threat? What is so bad about wanting to see more women or PoCs or whatever in fantasy?
Answer: not a damn thing.