Okay I’ve just thought of something, but Obi-wan says his pupil was called Darth Vader. As in that was his first and last name, a normal name. Not some dumbass evil moniker like every other dumbass red saber swinging goof in the universe.
That wasn’t changed by the prequels though, it was changed by Return of the Jedi. Obi-Wan reveals that Vader’s real name was Anakin Skywalker, resulting in the implication that “Darth Vader” is a code name. If you’re looking for a part of the Star Wars franchise that the prequels “OBJECTIVELY RUINED FOREVER”, that’s not it.