Ok but Empire Strikes Back and Revenge of the Sith are two of the most loved Star Wars movies in the community and they’re the most dark and depressing ones.
Read the 2017 Vader comics. Once you do you’ll realize how much story potential that era has, especially for Darth Vader. It was him at his prime, when he was younger and actually fought people that were somewhere near his league. It’s also a great opportunity to explore his inner psyche. I’d kill to see that in a film. Hell, straight up make a movie adaptation of the Fortress Vader story arc (which in my opinion is by far the best Star Wars story not in the movies, and I’d say it’s better then most of the movies). That’s literally the perfect Vader story.