Isn't the Witcher set in a wholly fantastic, non-European, realm? Like, obviously to some degree inspired by European fantasy, but it's not like there's an America to go to and bring back the potato from.
The Witcher is my specifically chosen example because people famously lost their minds about the Netflix adaptation moving to cast characters in it as nonwhite. ...because It Is Supposed To Be Based On Medieval Poland, Of Course. So you can see the weird tensions around the "historical accuracy" of fantasy – people have strong reactions, pretty high-stakes stuff.
(If anyone is considering commenting about their opinions on this kind of casting being Good or Bad, let's not – the point is that the Witcher's "historical accuracy" is something people have a lot of feelings about.)
Fun fact, Andrzej Sapkowski only specified a few characters' skin color when it was important to note that they were from the same region as Geralt of Rivia. Otherwise, the only big note is that Zerrikanians have sun-blackened skin (as in deep black like you'd find in many parts of central Africa). Everything else is basically just commentary on hair styles and especially hair dyes. Very little time is spent in his books discussing natural hair colors or skin color with the exception of people very far to the north, Geralt, and the Zerrikanians. In interviews back before the video games were made, (I'm going to paraphrase here), he basically said that the skin colors and hair colors were as diverse if not more diverse than Earth and because of the ease of travel for anyone aided by magic users, you could expect to find tons of diversities in any of the cities and even in large towns. As for the magic users and witchers, they'd be as diverse as the world itself as they were trained from all parts of the world.
When the media is based around folklore from a particular region, it's understandable to want it to match the region. I don't care about the casting, but if there were redcoat musketeers and samurai-looking warriors in a movie loosely based on old German fairy-tales, it'd be weird.
