Sampras, Federer, Djokovic and Tsitsipas are from 4 different generations of physical primes.
This means in every decade there are a set of athletes who are best suited to win that decade, the athletes from the prev decade or from the other after that cannot be expected to win a lot.....
1990s - Guys born between 1967-1972 were best suited to win, among these guys (Andre, Pete, Goran, Stitch, Krajicek etc etc) it was Pete who was best suited to win and so won most slams.
2000s - Guys born between 1977-1982 were best suited to win, among them (Safin, Roddick, Federer, Hewitt, Nalbandian) it was Federer who was best suited and so won most slams (15).
2010s - Guys born between 1987-1992 were best suited to win, among them it was Novak who won the most Slams (15)..... Nadal born 1 yr before this group and also being a Teenage prodigy he peaked early (physically) and started winning the french nd other slams early on so a part of him fell in the 00s too.
2020s - Guys born between 1997-2002 are best suited to win, TsiTsipas, Zverev, Medvedev, Felix, Sinner etc etc ...
What everyone needs to note is that, 1990s teens all turned pro in the late 90s and those courts were low bounce and superfast, then they adapted their games after 01 as the courts were relaid, compared to this the 2000s teens all turned pro by the mid 00s and till then they got like 5+ years of their teenage years to play on the modern day high bounce courts where rallies are longer, so they developed the muscle fibers for this before they turned pro. Thats why when Andy, Novak and co turned pro the Safins, Roddicks, Hewitts all started to fade away and Federer himself lost his invincibility.
Now, If Federer was born in 1987 (same year as Djokovic, Murray) then the person who suffers the most from all this would be Djokovic.
Nadal would still will all his French Opens but Novak's non clay slams would mostly be taken by Federer. Reason why we have a Big 3 instead of a Big 2 (Federer+Nadal) is because Federer can be tired out by Djokovic by taking the match to 5 sets and then somehow pulling off a win and making Federer look weak mentally, however if they were of the same age then those 5 setters would all be 3-4 setters with Federer winning. Plus Federer would be hitting harder than what he does now, his backhand also might be better equipped (might be a double hander) and he also might be using a bigger raquet early on, playing teenage Nadal would not be very good on but then he would adapt sooner and once he did, Nadal would be toast. Remember Federer before 03 used to lose to Safin, Hewitt and many guys, same as Novak losing to Nadal before 2011, but once these athletes reached their peak they were unbeatable for anyone in their age group.
So we now have a Big 3 because Federer is from the 00s and the other 2 guys are primarily from the 2010s, but if Fed also in the 2010s group then Novak suffers a lot.
Slam counts (over a 12 year period - say 2008-2019) would be.
Aus Open - Federer 6/7, Djokovic 6/5, everyone else 0..... thats right.... I dont think both of them can be beaten back to back.
French Open - Nadal 12-13 (he starts winning from 05 itself), Djokovic/Federer winning those 1-2 slams in that year when Nadal misses due to the law of averages... probably Stan can also get a win? ...
Wimbledon - Federer 9, Djokovic 1, Nadal 2 (2008 and possible in 07 as well) ...
US Open - Federer 5, Djokovic 3/4, Nadal 2 (those 2 easy USOs from 2017 would vanish from his tally) (This would be the closest fought slam between the 3 guys)
So total ....
Federer - 20-21 Slams
Nadal - 16-17 Slams
Djokovic 11-12 Slams
Stan and Murray would be on 0 or 1, even Del Potro might take that 1 09 USO ... Murray can beat Novak on Grass but can't beat Fed, Stan can beat Novak but not Federer, on clay Nadal cannot be beaten by anyone from any era, so that leaves them all with 0 Slams, hell Murray even if he was in the 00s his slam count would have been close to 0, I dont see Federer allowing him to win any slam and even Safin at his best wouldn't allow Murray to win.