Interestingly Black Panther/Wakanda was mentioned as being diverse, but is it really? Unless the new definition of "diverse" is now just "not white". Wakanda is entirely populated by black people. How is that diverse? Now from my own perspective this is not a problem at all. It is an insular nation in Africa. Why would they be anything other than black? Likewise Disney's live-action version of Mulan has probably the least diverse cast in modern history. Go look at the casting page. They are all Asian and as far as I can tell they are not just Asian, but almost exclusively Chinese. Again, for me this isn't a problem when you are representing ancient China, but it is not diverse!
There has been some recent criticism of Final Fantasy XVI being all white. Keep in mind that this is a game created by a Japanese company that has no Japanese people represented in it. But because it is an insular society based on medieval Europe where everyone is white it is "bad", but Wakanda, an insular society in Africa where everyone is black, is "good". That's a double standard isn't it?
Not really.
There are, in my rough estimation, ten billion Marvel comics that have been turned into movies or TVs. Most of them are very white.
One movie (well, two, since Black Panther has a sequel) and
one TV show (Luke Cage) have almost-entirely-Black casts, as far as I know (I fully admit to not seeing a huge number of their movies or shows). And in both cases, it makes sense in-universe--especially in Black Panther, which
is an insular society that has deliberately had limited contact with the outside world for basically ever. And Luke Cage takes place in Harlem, which until recently was a predominately Black neighborhood (the current census puts it as a Latino majority).
Whereas with a show like RoP, it appears (from what people have been saying) that there has been a slow but constant mix of cultures for hundreds of thousands of years. Harfoots apparently travel quite a bit. There have presumably been traveling merchants, maybe even merchant caravans, going from place to place. People have explored. There would
be a mixture of cultures and skin colors. And probably to a greater degree than you might think, since unless the writers actively decide that one group thinks they're better than other people because of their skin color, then there wouldn't be nearly as much discrimination and people would be more welcome in other places.
Also, from a meta-perspective, up until very, very recently, everything was geared to white people. Many or most shows, movies, and comics didn't have
any non-white people in them as main characters, or even as secondary characters. A lot of them didn't even have
women except as disposable love interests (and definitely not any non cishet characters). This wasn't even necessarily for racist or sexist reasons--the media were created by people who were white men who were catering to the demographic they were in. Which means that these white characters were only white or male by default, not because they were
supposed to be white or male or because white maleness was an integral part of the character. Changing race doesn't actually change the character, and in many cases, neither does changing sex, gender, or sexual orientation. Maybe it would be slightly weird if DC decided Bruce Wayne was Black or Latino, but
only because he's supposed to come from
old money, and there weren't a lot of billionaire non-white people a hundred years ago. The
rest of his story would be the totally same, however.
But when creators (both white male and not) and created non-white, non-male characters, they did so deliberately. Black Panther and Luke Cage are
supposed to be Black, and turning them white
would change the characters. Adding in white people to Wakanda
would change that country beyond what it was supposed to be, and adding in more white characters would dilute the story's intent.