While I love tennis, looking back in history, I think it's pretty disgraceful that it only became fully 'open' from the late 70s or so. It was bad enough that the open era started as late as April 1968 with separate amateur (though they were paid money under the table) and professional tours for the men before then. But even during the early years of the open era things weren't fully 'open' yet with players being banned from entering certain grand slams based on their affiliaitions, for example Laver wasn't allowed to defend his Australian Open and RG titles in 1970 (though after winning the grand slam in 1969, his priority understandably switched to trying to earn as much prize money as possible before he retired), and Connors travelled to Paris but was banned from entering RG in 1974.
That makes it's difficult enough to compare players cross generations. And as grand slam counting only became a huge from the 90s onwards, I don't seen the point of comparing the big 3 with any players pre-Sampras.
But in terms of comparing the big 3 amongst themselves, I already think that Djokovic is already greater than Nadal as things stand, and if he wins today he'll move out of sight IMO unless Nadal can somehow put together an insanely dominant and legendary season at the age of 37/38 in 2024 before retiring. If Djokovic had won the 2021 US Open final against Medvedev to secure the calendar year grand slam and holy grail, I think he would have ended the debate vs. both Federer and Nadal there and then. Thankfully he didn't, but I think he can do that today. I hope Ruud somehow upsets the odds and beats him though.