This is sure reading a lot into an unpublished letter that just says he disliked Dune without giving a reason. Maybe he hates sand, I hear some people do. Maybe

This is sure reading a lot into an unpublished letter that just says he disliked Dune without giving a reason. Maybe he hates sand, I hear some people do. Maybe he thought it was too long and should have been split into three volumes. Interesting way to discuss some related issues, but, like Dune and Tolkien's own work, highly speculative!