I think people place too much emphasis on the "slowing down of the courts", and even poly strings.
We know that tennis players, on average are better than ever. Nutrition, exercise, training, commitment, are all much higher than they used to be. But it's also the case that tennis minds now incorporate rudimentary knowledge of physics and mechanics for producing optimal strokes, and utilize video for optimal strategies in learning "what works". Bollieterri revolutionized the game by training players in optimization and honing out inefficient, diverse techniques. It took time for the old guard to die out, but they did some time in the early to mid-2000s. But we know even by then, S&V was a failing strategy, that lost more often than it won. Safin and Hewitt decimated S&Vers as a matter of course. Fed had to abandon the technique to become dominant.
There were once bizarre things you could do and still be a top player. You could have a Borg half one hand half two hand push release backhand. You could have an all-wrist continental McEnroe forehand. You could have a Michael Chang serve. Those things were low-hanging fruit that subsequent players could easily exploit, hence you don't see them anymore. S&V was mid-hanging fruit, but evolution has tapped it out.