Frankly the fact that Medvedev and Thiem are the best of the bunch is in itself an indictment of the generation. Thiem while pretty good physically is one dimensional and doesn’t think the game that well, while Medvedev thinks the game well, moves well and serves big but his unorthodox strokes leave him somewhat physically limited. Of course relative to the pack they’re great but it’s not just the big 3 - I don’t think they’d have been beating past greats either. Neither even has the ability to bring what inconsistent guys like Safin/Stan/Delpo brought on peaking days.
Tsitsipas has a pretty good game but seems like a bizarre person with his twitter philosophy and blogging, and not ruthlessly focused on winning like past greats. He also has no return, which you can’t really win without.
Zverev actually has the closest thing to the game needed to be a champion, but has had all kinds of mental and personal struggles. He has the big serve, movement, strong off both wins, and unlike the rest of NextGen has a good return. Net game needs work but he has the tools for success in modern conditions.
But one of the things with the big 3, Sampras, and past greats is they’re all in the conversation for ATG level weapons, whether serve or return or a particular groundstroke. Which young players even have 1 ATG level weapon? The Kyrgios serve comes to mind, but he doesn’t have the rest. People talk about Rublev’s forehand but it’s not versatile.
Young players in other sports don’t seem to struggle as much to develop the mental aspect of the game. Maybe because the development system in big team driven sports is much more structured and less independent.
If we look at the timing of the huge drop off, basically Delpo being the last of a strong generation, it’s the generation that grew up with poly, lower swing weights, homogenized courts that had failed. The other confounding variables are that they’re the generation that grew up with social media, and they make quite a bit more money for their mediocre results than past players - both could affect drive and focus.