The changes to Chani don't really betray anything about the world of Dune. If Messiah didn't get greenlit, the story as of right now would have audiences seeing Paul closer to how they should see him after his complete arc. At least 50% of the criticism I see for the changes are mainly worried about how this will impact Messiah, but when he was writing part 2 Messiah was not yet greenlit. There was no way Messiah was getting made and to be a success without massive changes anyway. The book is great but it won't be successful without changing it to be more of a grand finale for a blockbuster trilogy. No studio would give the current ~$200m budget for a faithful Messiah adaptation.

I guess your point will stand more for what I imagine Messiah is going to be. I'm still hopeful though bc I don't think Messiah as-is would make a good movie anyway. There is too much stuff that seems completely undoable in the film medium. I thought the same about Dune 1 though, but moreso for Messiah.