Boris does have some good points, but at the end it's how much you win, like any other sport. The problem in tennis is that, and God knows how many times we talked about this, it is almost impossible to compare different eras. When I started watching tennis, as a kid, Borg was my idol and I still think he is the best one. he quit when he was only 25yo.
If you look at tennis history, we have Laver, we have so many 'old' players who were playing tennis and winning for 20 years or so at that time. I wasn't able to watch those players except for some odd you tube videos. people have a short memory.
then, the open era, pre open era. it gets too complicated. just my 5 cents.