Not convinced by your argument at all. You seem to suggest that the entirety of the tour became weaker, thus allowing Anderson and Johnson to shine and the Big-3 to remain at the pedestal. Isner broke into top 10 in 2012, so I wouldn't consider his success recent, and if you watch Anderson's matches in the year where he made it to the Wimbledon and US Open finals, it was obvious that he had elevated his game to a new level, not that his competition had weakened. That the Big-3 are still competing for slams is a testament to their greatness rather than the tour's "weakness." When I see Djokovic and Nadal now play, I don't notice much of a decline in athletic ability, not in the same way Agassi had visibly declined by the end of his career. Federer is admittedly slower on his feet, but the reflexes are still amazingly there, and he's constantly adapting his game to compete against more physical youngsters (playing more S&V etc.).