From 1975 to 1990 before Pete Sampras burst on the scene, John McEnroe and Bjorn Borg were the two most talented players I saw. McEnroe, from the standpoint of shotmaking variety, volleys, and uniqueness and placement of serve, was the most talented player I ever saw. Borg, in his era, was the master of fitness, groundstrokes, and topspin. McEnroe won 7 majors; Borg, in an abbreviated career, won 11. McEnroe's number of majors was extremely low in relation to his talent, for a myriad of reasons, including mental issues including burnout and exhaustion, and over-dedication to Davis Cup. His 1984 season in which he went 84-3 has not been matched.
In 1990 Pete Sampras burst on the scene. He had a tremendous power serve and was a very skilled serve and volley player. He won 14 slams. He did have, in my opinion, the best competition during his era that we have seen, which included Agassi, Courier, Chang, Edberg, Becker, and many others. He won 14 majors against better competition than what Federer, Nadal and Djoker had outside of each other.
I don't believe Federer, Nadal or Djokovic were more talented than Borg, McEnroe, and Sampras. I think they benefitted from the top tier of tennis being weaker, for a longer period of time. They are ahead of the other 3 in numbers of slams, but I do not know that they were necessarily better players.