I disagree. The book takes the approach of framing it as a mystery and is primarily from the perspective of the FBI investigation. But I think focusing it in on the relationship between DiCaprio and Gladstone's characters works so much better. It's not so much about a sheriff riding into town but instead about a family and community being ripped apart. With the ending, the film is basically in conversation with itself and other pieces in that genre about how those stories are told.
Changing the perspective doesn't limit the scope of the story. Quite the contrary, it could have given us a glimpse of the community which was direly needed.
Instead the film is told through the perspective of Ernest Burkhart, an outsider simpleton who keeps saying yes to the atrocities the devilish uncle tells him to do. The Osage characters are paper thin, the sisters and their family are non-existent, fodder for the audience to pity. The one who gets screen time her only feature is being promiscuous, the main character spends the film in her bed or stoically looking into the horizon and there's a guy who's sad all the time. This is Osage in Flowers of the Moon where random criminals are more fleshed than the tribe.
It's not about a community being apart, there is no community, no inside looking into the Osage nation, their culture, their relationships, their history. Its a story about a bunch of detestable people doing horrible shit for 2+ hours and then law enforcement shows up and stops it. The final act of the story explores the machinations of the villains trying to get acquitted of their acts. It's not about the family healing or the tribe reaction, because they don't exist in this film, only Ernest pov of them. We actually get Ernest verbally explaining to his uncle that they now hate him, in case the audience still had any doubt.