This. At the rate at which compe ion is (not) coming in at the lower levels (as the best European athletes go into soccer, America just stops producing good players due to lack of interest in tennis and losing athletes to more lucrative sports, and people in general opting out of sending their children to draconian tennis training schools from social pressure); we are guaranteed to see a very high performing group of people who should be getting their asses handed to them by dint of their age keep being able to
persist against a wretchedly unskilled lower generation.
In a healthy era, the slam count of the big four would be HALVED, easily, and we would see Federer with 9 or 10 slams, Nadal with 7 or 8, Djoker with 5 or 6, Murray with MAYBE one. It is unlikely that any would have a career slam. They're all very good players, but the numbers they are putting up reeks of a bad younger generation and it's being proven that this is the case as time goes on; and NOT that we are just lucky enough to see a bunch of all-time greats at the same time.