I see it more like the planet of the apes movies. Essentially what ends up happening when they travel back in time changes the future into a peaceful one, and (at least personally) I don't think it took significance away from the events of the previous films, even though it basically undid everything that happened in the first two films.

I understand the beef with X-Men as it was basically just ret-conning the previous canon because people didn't like them and to make way for the future stories they wanted to tell, but I don't see this as being that way. It would be the ending of the story of Luke's journey and more the idea that the events of the OT were essential to getting Luke to the point where he could do this and helped prepare him for the trials he would face in the PT era.