slams
nole 24 (+4; +20%)
fed 20 (+6; +43%)
sampras 14
This is not entirely accurate. Some additional context will explain why this factor is actually a reasonable argument for Federer's GOAT status, at least for those who view winning slams as the most important measure of greatness.
There is no dispute that Djokovic holds the all-time record for most slams won. That's an objective fact. So if one's rubric is nothing more than, "Slam record = GOAT," then Djokovic is the GOAT. This is a simple and convenient rule that, among other things, will tend to ensure that the GOAT is a current or relatively recent player, not some relic from eons ago, since records move in only one direction. But note that the choice of GOAT criterion or criteria is subjective, not objective. (I am not arguing that the slam count is the only tennis stat working in Djokovic's favor. The topic of this post is just limited to the different ways the slam count stat can be viewed.)
Here's a more complete look at the progression of the slam record:
Tilden -- 10
Emerson -- 12; +20% (2 absolute)
Sampras -- 14; + 17% (2 absolute)
Federer -- 20; +43% (6 absolute)
Nadal -- 22; +10% (2 absolute)
Djokovic -- 24; +9% (2 absolute)
The degree to which Federer extended the slam record is far in excess of anyone else's extension, in both relative and absolute terms. Does this matter? It does if one believes that the essential mark of greatness is how far beyond the previous standards an athlete can progress. According to this view, extending a record far into unknown territory can be more important than ultimately holding the record, especially since future performance naturally tends to build on and surpass past performances.
Here's an example from another sport. Babe Ruth is still considered by some as a candidate for the greatest baseball player, greatest slugger, and/or greatest home run hitter ever, even though he played a century ago and his most important record was broken a half-century ago. This is because Hank Aaron (we'll leave out Barry Bonds and his steroid stats) beat Ruth by about 6% when he extended the home run record from 714 to 755. But the HR record before Ruth was 138. Ruth more than quintupled the old mark! That's an increase of more than
400%. (The "dead ball era" was a factor here, of course, but so was a quantum leap in player excellence.) Nothing like that had happened before, and nothing like it has happened since. I'm not suggesting that Federer's improvement of his standard was comparable to Ruth's, but it's true that being a pioneer, and pushing a sport far beyond its previous performance boundaries, is often recognized as an important factor in determining greatness.