Before the concepts Representation and/or Cultural Appropriation were talked about, Hollywood would just hire a Native American scholar or cultural consultant, who would work with the writer (whatever their ethnicity) to make sure the depiction was authentic. I guess this is similar to a sensitivity reader, but the consultant would only be an adviser--they would not have veto or censorship power over the script. This is because writing is a talent that only a small number of people can do really well. While the consultant knew about their ethnic background, they did not necessarily know about writing or the movie business. That's a whole different skill set. It's important to get someone who can write, and do it on time, since movies cost millions of dollars to make. If the writing is bad, the movie can end up bad, and it won't make it's money back (ie: the price of failure is very high).My question here, is who is sad? Who is objecting?
If Native Americans are frustrated with their portrayal in westerns, it's probably better that writers find something else to write their westerns about if they can't seem to nail the Native American perspective. Yeah, that means they don't get the representation they used to, but no representation is better than bad representation.
That representation might even be well-intentioned, but if you get it wrong, you've still got a bunch of cringing, ticked off Native American viewers going "where does this guy get off pretending like he understands us?"
This is why we do our research and use sensitivity readers and not assume our good intentions will protect us. Imagine being the only Native American watching a western movie and seeing how absolutely wrong the writers got the details of your culture, that they could have found out if they had only deigned to ask... and meanwhile the rest of the (white) audience is just sitting there watching the movie going "Yes, yes, this is fine. Aren't we so enlightened with our sympathetic depiction of Native Americans?" I would want to claw my eyes out.
Some movie-specific problems to consider:
1) Finding a good Native American writer who is free to work on your project. Hard since, there aren't very many, and they might all be working on other projects.
2) Find a writer who wants to do the job. Even if you find a writer, maybe they just want to write a book, or aren't interested in telling the story you want them to write about, so they turn the job offer down.
3) Find a writer who is the right fit. Sometimes people don't get along or argue, or are unreliable--if the writer can't get the job done on time, or constantly fights with the producers, then don't hire them. Let's face it, some writers are just bad, and having the right ethnicity is no guarantee of quality (much less, a finished screenplay).
4) Even if you find a writer with the right general ethnicity, they aren't necessarily an expert. For example, you are producing a movie about the Iroquois in 1705, and the writer is Sioux with no history training, the writer isn't going to be an expert on the right tribe, or know their history--being Native American is not a guarantee of expertise. Worse, some Iroquois could see the film, and be mad that the Sioux writer got it wrong.