one thing that does ring true

The upper classes in Britain did routinely send their boys away to their father's school at a tender age. It ensured the "correct" accent, ideas, and connections. Most of the world, including America, thought that was bizarre. Combine that with the Depression-era dislike of training an all-American little boy to be a snobbish member of the idle rich and audiences lost all patience with this film.

If the hero had come to appreciate what he found in America and resisted all attempts to make his son into a landed aristocrat, it might have gone over better but it wouldn't have been true to life. The whole point of being an aristocrat was tradition, just as the whole point of being a Native American was tradition. The whole point of being American was adapting to life as you found it with little regard for the past. You couldn't find a more deep-seated clash of cultures. The hero wanted to raise his son to be like him, the heroine wanted to raise her son to be like her, and the audience wanted him to be raised like them.