A sliding time scale with Superman would be a blessing, but they rip out Stories and character ideas with Superman. The Legion of Superheroes debut in a Superboy adventure, their part of his story but I have read so many justifications why Superman shouldn't even interact with the Legion. That's different than just changing dates. For me it's more like reading how the Sinister Six shouldn't be Spiderman villains or Galactus shouldn't interact with the FF. And I would go so far as to suggest it's like saying the Fantastic Four are better off without Reed. Ask any fan mourning their Superman, "Why they always taking away my Superman? And who's this guy?"