I feel like the Death Star existing at all ruins all of Star Wars, from a certain point of view.
The Americans have built (and used) the nuke, what does everyone else do? They build their own, of course! Why doesn’t the Republic start building Death Stars after VI, or, better yet, why doesn’t the Empire build like 20 after their rise to power? Realistically the sequel trilogy should be about two sides having nuclear bombs pointed at each other yelling.
But it’s Star Wars, so it doesn’t need to make realistic, logical sense. The expanded universe tells us all the reasons that this doesn’t happen. Moviegoers don’t get that info, but they don’t care because the story is about the characters.