Book Dorne was a giant shaggy dog story that results in a kid getting sliced up (not great for reviews and very costly for makeup for her remaining appearances) and, last we know of, Jaime on his way to maybe tell her she is an incest baby but it's cool because all these people on reddit/lemmy see no issue with that. So she is all but guaranteed to die horribly upon returing to Westeros but in the arms of Jaime.

Show Dorne led to Myrcella getting dead and had the god awful "everyone wants bad pussy" line or whatever it was. Which was obnoxious but very much lines up with the sexposition of the good years that people seemed to love.

I think a better argument would be Lady Stoneheart. As a character, she mostly treads the same ground that Thoros of Myr and later Jon would (all of which almost assuredly ends with "but who cares about magic because the real evil is humanity"). But all signs are that it drastically changes both Jaime and Brienne's arc. That said, I assume show Jaime ends up being much more sympathetic (and, thus, tragic) and Show Brienne likely merged with another character to become the new head of the kingsguard as a way to give her story a better ending than "brainwashed by birgands and dead in a ditch".