@Jaded I've only ever heard good things about Anya Charlotra's portrayal of Yennefer. Personally I think she's the best part of the whole show.
there's also the Polish fandom, which in general wasn't positive toward any race bending
This I've caught. While part of that is surely a touch of old fashioned racism; the Eastern Block isn't exactly short on it, it also seems a bit more complex. Something along the lines of not wanting to get caught up in the American race and diversity politics, when in Europe its Poles who have gotten shit on for centuries, and this being their time to shine and be seen. As opposed to being portrayed in ways to suit American sensibilities. Anyone following Brexit'll have caught on the general 'shitty polaks coming to steal our jobs' sentiment simmering, and that's common enough across the board. From the Polish perspective, there's little conception of white privilege, or guilt, having had no slaves, no colonies, no empire, mostly just being victim to them. The places they're likely to go, they're the second class citizens from the second class culture (though its changing, at least where I live - white Slavs doesn't quite get the usual suspects' blood boiling like it use to, not when there's Syrians and Afghans - anything muslim really - and Africans to panic about). Its one of the most homogeneous countries in Europe, too, with the vast majority of migrants being from Ukraine (especially the Ukraine that used to be Poland) or other Slavic countries. So when its their fantasy culture on display, they're like to expect it to be pretty darn white.
Is that naive? Sure. Is there a bit of racism there? Yeah. Is adding a bit of diversity a sign of American Cultural Imperialism, or Cultural Appropriation? Heh. Though reading this one guy going on a bout it made me chuckle, and I've been searching for that article (or blog post, or whatever), to link, but to no avail. But there are some complex currents working through the responses that I've found interesting to read and ponder a bit on.