Sampras obviously. When he retired many had him as the GOAT, even over Laver. All his records being so easily bypassed by Federer, Nadal, Djokovic have him not only seen behind those 3, but by nearly everyone behind Laver now (while when he retired many had him above Laver, but almost nobody does anymore) and Gonzales too now, and quite a few also have him behind some of Tilden, Borg, and 1 or 2 others as well now. He basically went from possibly the consenus GOAT to the bottom half of the top 10.
On a lesser scale that might wind up applying to Federer. He could wind up going from the almost undisputed consensus GOAT to being generally seen as 4th or 5th only all time, with many already now seeing him as only 3rd best player of his era. I know I have said I personally feel he is better than Djokovic and Nadal still, but that is definitely a minority viewpoint already, and will likely become so even more in the future.
In many ways Laver's legacy actually improves over time. Even with all the seemingly untouchable records falling easily nobody can duplicate his Grand Slam, even if he regard his 69 Grand Slam as the only legitimate one, nobody can even duplicate that. All the other records are falling right and left, but that one can't be touched. Djokovic couldn't attain it even in the godawful 2021 field, proving how difficult it is. That he was almost never headed as top dog during his 7 year or so reign while Djokovic, Nadal, Federer have all spent years trading back and forth top honors, also makes him look even better. I see him as a rare person who will almost never be out of the GOAT race entirely.