DMP, Thanks. I agree to a great part. Yes, tennis has changed a lot. I still claim that most of the current very fast game is owed to modern technology.
I would say all of the modern game is due to technology
Nevertheless many people including me are trying to make all-time rankings.
I only would contradict a bit that amateur tennis in the 1960s was highly significant. I do know that the organizers of the Slam tournaments eagerly wanted to get Laver and Rosewall which means open tennis ("butter instead of margarine").
I think by the end of the 60s both sides wanted an agreement. The pro circuit wasn't in the best of health. There was little new blood because the top amateurs were getting by nicely with 'shamateur' payments. Change was in the air. In the early 60s the pro game was much healthier, especially with Laver joining them. By the end it was looking a bit tired and the excitement was transferring to the amateur game.