As a potential heir to the stewardship, Christopher Tolkien was very much alive at the time the movies were being made and was famously opposed to a lot of the artistic choices being made.
Rowling apparently maintained some artistic control on her movies, whereas Tolkien had sold the rights entirely, so Christopher didn't have much of a say beyond complaining.
I think the thing that really "solved" it for me was realizing that the vast majority of the people who watch LotR will never read the book, let alone the Silmarillion. And those who DO decide to read those after seeing the movie - the movie won't destroy it for them.
"Stanley & I have agreed on our policy : Art or Cash. Either very profitable terms indeed; or absolute author’s veto on objectionable features or alterations."
I don't think it was explicitly stated there, but I think it is clear they went for "cash". Though I recall some of his letters saying that the unexpected success of LotR meant that he wished he'd retired earlier. It was clear that there was a lot of financial struggle in his life, but that's not to say he wrote for the money of course!
I think the thing that really "solved" it for me was realizing that the vast majority of the people who watch LotR will never read the book, let alone the Silmarillion. And those who DO decide to read those after seeing the movie - the movie won't destroy it for them.