The fact that ROTJ confirms that Anakin and Darth Vader are the same person contradicts your idea. There is no mention that Anakin took the identity of someone else: he became Vader, he didn’t remplace him.
It doesn’t contradict my idea since nobody ever says he DIDNT take up someone else’s mantle. Does it involve a little retconning of what everybody THOUGHT based on what was said in the movie, yes, but it doesn’t directly contradict what was said. I understand your point. It’s not perfect or ideal, and you’re against preserving the reveal in the first place, so it’s a bit harder to get u on board, but it’s just the only way I can think of that fits the OT and preserves the reveal without making the audience feel like they’re missing important story points.