True, there is a line you can go over when adapting a book to a movie.I would agree with you in some cases. As said above, I could not get into the books at all, so I am stoked to have been presented with Villeneuve's adaptation, which I have enjoyed immensely.
However, there are some literary greats whose work should not be adapted. Take Tolkien as an example. The LOTR films were excellent and kept largely to the books. The Hobbit, on the other hand, is only a small book which was stretched into three lengthy movies and Jackson took pieces of The Silmarillion to role into an epic story. Was he right? I am not too sure, but I still enjoyed it.
Herbert, like Tolkien, created a detailed universe that that leaves one in awe. To me, Herbert lacked the story-telling capability of Tolkien, and that is where Villeneuve's brilliance comes in to play - to present an immensely enjoyable view of Herbert's universe.
I am tempted to mention GOT, but Martin himself is responsible for how that turned out by not finishing his own story.
Jackson's version of the Hobbit was an absolute abortion of a movie(s) probably driven by the $$$ to get three rather than one 9maybe 2) at best.