Let's see. 60 G.S. between the three champions since 2003 Wimbledon (won by Federer) on the one level is awesome but what does it say about the men's competition during those 17-18 years who lacked the progression and mental strength to challenge them consistently, especially when you compare it to the competition of bygone era's ?
I've come to the conclusion that there are a few factors involved with this crazy phenomena of dominance by the Holy Trinity.
1. They're all better than anyone else. Individually, these are the three best players we've ever seen. They are capable of levels of tennis that no one else is, except for short moments. Really, the only guy who has come close is Stan Wawrinka and maybe Andy Murray (Andy was more consistent than Stan, but I don't think was as good as Stan at his best). And Stan really only did it for a short time and even then, was inconsistent.
2. They all have incredible longevity. You have to go back to Laver to find a player as dominant over a long period of time. The all-time greats of the 70s-90s all had dominant spells, but not for as long.
3. The generation after Rafa/Nadal (Lost Gen) was historically weak. No Slam winners from players born in 1989-92, and only Grigor Dimitrov and Jack Sock won big titles.
4. The Next Gen is better, but not great. If we say that Next Gen begins with Dominic Thiem (born Sept 1993), it is significantly better than Lost Gen, but with no clear all-time greats emerging.But there are a lot more big title winners: Thiem, Zverev, Medvedev, Khachanov, Tsitsipas, and Hurkacz so far. I would compare this generation to the one between Sampras/Agassi and Federer, that included players like Kuerten, Moya, Rios, Costa, etc. A bunch of guys winning a single Slam and/or multiple big titles, but only one guy (Kuerten) with three. Or to put it another way, between Sampras (b. 1971) and Federer (b. 1981), or 1972-80, only three players won multiple Slams, and none more than 3: Kuerten (3), Rafter (2), Safin (2).
When you combine all four factors, you have three 20 Slam winners.
I do think Next Gen will win more Slams. It is hard imagining that players like Medvedev, Zverev, and Tsitsipas won't win at least a Slam or two. But I highly doubt any of them reach the sacred 6+ mark that separates the ATG from the lesser greats.
To get to our next 6+ Slam winner, I think we have to look for the "Millenial Generation" - those players born 1999 or later. the most promising of the bunch so far seem to be Denis Shapovalov (1999), Felix Auger Aliassime (2000), Sebastien Korda (2000), Jannik Sinner (2001), Lorenzo Musetti (2002), and Carlos Alcaraz Garfia (2003), maybe one or two others. IMO.
But those players above are between 18 and 22 years old, so only Shapo is entering prime years.