Nadal is pretty debatable as clay GOAT. Borg had almost as many FOs until he got sick of being spanked by McEnroe on fast courts and quit, he would have ended up with quite a few more. I am prepared to give it to Nadal but it's not like its a closed discussion.
The nature of the tour has changed significantly, a lot of records aren't really comparable between eras. Djokovic getting the same slam counts as Becker and Edberg is meaningless because it was much harder to dominate in their day. Just because strings, balls, surfaces have made upsets much less likely doesn't mean that modern players are better than past players.
Modern players are also stronger,faster more prepared in essence a better version of past players.......this is tennis how it should be......Djokovic is better than Becker ever was...Nadal is better than Borg...Federer than Sampras......it's the way it works