So MT, I am actually saying that there have been no technological changes to tennis in the past 20 years that have significantly changed the game.
I agree with you that current use of poly strings have changed swing paths tremendously, but as I said before; Kevlar gives you the same kind of dead feel. That's what Agassi used. Bjorn Borg strung his racquets at 80+ psi. The frames would break in his bag flying from one tournament to the next. But stringing at 80 psi gave him the same kind of dead feel that poly gives players now. It took tremendous talent to be able to play that way. I agree with Masterclass that these larger frames make tennis an easier game. It's still takes talent, but not as much as in the past.
In fact poly is not a new technology. It was introduced to tennis in the 80's, but got completely ignored at that time. Probably because it's a dead string, and sweet spots at that time were only just beginning to get bigger.
My comment originally was to point out to Babblelot that given the technology that Agassi and Cash were using during their US Open match in 1997, had they learned to play using that technology, the match would have been very much like tennis is played today.
There have been some minor developments in technology, but nothing that has changed the game like larger frames with bigger sweet spots. Regulate that and you will get your serve/volley game back. Eventually.