I do think the introduction of a black, female president of MACUSA is a new/recent element that is problematic within US history. I do think some of what Rowling has tried to say in the years since the release of the books and the original movies about Hogwarts and the magical world has been new information that in some cases is difficult to deal with.
I completely agree that in fantasy like Harry Potter, that is meant to take place in our world/with our history, there is always some suspension of disbelief required and some things aren’t going to make real-world sense. I just feel there’s a complete disregard of certain major issues that is increasingly problematic. I understand that there isn’t going to be a U.S. where, say, any notable portion of slaves were freed by a black wizard or witch. The X-Men, in the movies, didn’t radically change the course of history either. But there is a recognition of how is it that these very powerful people, who grew up “normally” until their powers manifested themselves in various stages of adolescence, dealt with being subjected to prejudices and oppression.
The X-Men is also more of an allegory generally about prejudice, which HP certainly was never intended to be. But I think the frustration with JKR is that someone who always took care with all the very unique and creative ways she built her fictional world is seeming to show less care on some major points. She wants to add diversity (and I’d agree she’s doing so with good intent) - great! But that doesn’t make it reasonable to simply say that the magical community in the U.S. was so racially ahead of the curve (gender-wise too!) that they can elect that president at that time. It makes it hard to understand the social history of the magical community in the U.S. Were magical people coming to the U.S. from Europe back in the day just without any racial/gender prejudices? How is that possible? It’s not like they were coming from diverse countries or communities. They arrived in what became a diverse country that overran the racially different native population, enslaved another race, did not officially give women the vote and other rights until way later, etc.
And again, aside from the majority population, it truly complicates things for muggle-born minorities. It didn’t need to be dealt with in the original books, because it was the 90s-00s, and there’s no real issue with the magic world reflecting the diversity of the UK/Europe at that time (even bettering it in some ways). Now, though, we’re in different countries, in different time periods. I know the social history of the U.S. is not the point of the books. But this is the direction JKR has chosen to go in. I’d like to see some acknowledgment of that - can totally be basic/brief/throwaway - in how the world continues to be constructed.