It's not a matter of historical accuracy. This is Middle Earth - it is a fantasy realm. It is a matter of understanding how ethnic diversity works. You cannot have people with dramatically different skin colours living in the same community unless some of the families of said community originally came from far away. This is basic worldbuilding, and you don't even have to do much to justify it - establish that traders are going through these communities, and you've thus established a mechanism for people to come from far away and join them. Notably, the show doesn't do that (in fact, it does the exact opposite - the non-elven communities are depicted as being isolated).
And what's truly galling is that the Harfoots are literally described by Tolkien as having darker skin. People may argue about what "darker" means in this context, but you can make them all shades of brown and then point to the text and say "this is supported by what Tolkien wrote," and be RIGHT.
Then you have the Easterlings, who are described by Tolkien and in the Tolkien wiki (I don't have time to look up the reference in my Tolkien collection) as: "Their skin was either sallow (a pale yellow) or olive, their eyes were dark (dark brown and black), and their straight hair was black." (source: https://lotr.fandom.com/wiki/Easterlings) So, they are described as being akin to the people who come from the Middle or Far East. You could cast all of them with actors from that area, point to the text, and say that it is completely justified by what Tolkien wrote, and be RIGHT.
So, you have three ethnic groups who have been presented in episode one. One is described in the source material as functionally being white. One can be interpreted as being shades of light brown. The third can be interpreted as being from the middle or far east. What did we get instead? With the exception of the elves, a mix of approximately 50% white, 35-40% shades of light brown, and 15-10% black (the elves are right now around 95% white, 5% black).
The show removed the actual diversity that was there, which was based on Tolkien's understanding of history in the real world, and substituted their own, which as far as I can tell was based on Southern California. As far as I can tell from the first episode, they didn't even establish any new worldbuilding to replace what they removed - I'm not sure there's any functional cultural difference between the Easterlings and the Harfoots other than one lives out in the open and the other stays hidden.
The show being in a fantasy world means that there is a greater onus to do proper worldbuilding, not less of one.
And what is the history of America? America has a colonial history marked by the displacement of the indigenous population instead of the subjugation of them. This means that when the continent was colonized, the colonizers moved there en masse with their families, and also imported ethnic minorities from other parts of the empire to do manual labour (such as slaves from Africa). The main characteristic of the colonization of North America is mass population movement into the area by people from far away.
Compare that to Africa or India, and, with the possible exception of South Africa, you get a type of colonialism marked by the subjugation and exploitation of the indigenous population, not their displacement. The colonizers tend to live in small enclaves, which may or may not relocate out of the country when colonialism in that area ends. So, yes, you will get towns in America populated by ethnic minorities with a dramatically different skin colour. But you're a lot less likely to see them in India, or China, or Japan, or sub-Saharan Africa. America is an outlier when it comes to ethnic diversity in the world, not a rule. Everywhere else tends to look a LOT more homogeneous.
I'm sorry, but the argument you are making holds no water.