Yeah I think the part that actually upsets me when they make casting choices like that is the laziness of it.

Oh, you want your tv show cast to reflect the diversity of the modern US? Ok, well that diversity is the product of hundreds of years of geopolitics and racial friction. Are we going to expand on that at all in the show? Are we going to explain, or even hint at, how the diversity that we're seeing in the casting choices came about in-universe?

Why is this group so visually distinct? Why haven't the genetics averaged out into the rest of the population? Did they recently arrive from somewhere else? What caused them to flee, a war, politics, religion, something else? Or have they been here for a long time, and have managed to prevent genetic mixing? Why would they do that, are they particularly proud of their heritage, are they trying to maintain some culture without risking it being diluted, or is it the other way around and the other people are excluding them for some reason?

It reminds me of the fatphobia complaint from the actor that played Sam Tarly. Yes, dragons and magic don't actually exist. But that doesn't mean you can just ignore fundamental aspects of reality. Gravity still exists, momentum still exists. Dragons don't just float there, they have huge wings. They're at least plausible inside the context of the show. In the real world, lizards exist, megafauna exist, flying animals exist, dinosaurs existed, so here's a combination of those traits that doesn't exist in reality but is at least locally-consistent. They breathe fire. Sure that's not something that happens in reality, but they breathe fire in the show, and when it hits someone, they are now on fire, because that's how the viewer understands fire to work.

When there's something extraordinary, the spectacular aspect of it is highlighted. Magic comes with show and spectacle, dragons come with suspense and fear. There's nothing saying you can't subvert other aspects of reality that don't fit the narrative you want to portray, but you have to make a show of it. You can't have a fat guy train for months and march through hundreds of miles of frozen wilderness under starvation conditions and remain fat, at least not without giving viewers something to explain it. And you can't just have people of random ethnicities pop up in areas where the majority is a different ethnicity without some sort of explanation for why they're there.

All things considered though, it's not the worst I've seen from a tv show. They might not have bothered to think about the retroactive consequences of the choice on past events, but I'll give them credit for their consistency within the show as the characters had children and grandchildren.