imo Borg would not have quit the game in 1981 at age 25 if McEnroe wasn’t around. Borg admitted it was all about being no.1 for him and no.2 was the same as no.20 in his mind. Borg was at his absolute peak in 1981 and only the genius of McEnroe could challenge him. Borg knew he couldn’t play any better and Mac beat him in 4 setters in Wim and USO finals. It broke him mentally. Borg in 1981 beat Connors in Wim and USO semis, the latter a very impressive 6275 63 thrashing (Connors went on to win ‘82 and ‘83 USOs after Borg quit). If Mac wasn’t around Borg would have 13 slams by the end of 1981 at age 25, and probably 14 as he would have played AO to win calendar slam. Actually very likely 15 slams as he prob would have won ‘80 USO (lost 64 in 5th set to Mac in final). Now imagine a peak age and form Borg age 25 with 15 slams under his belt already, and having just won calendar slam. How do you think he would have gone the next 5 yrs to age 30, and maybe played on a couple more yrs to 32 or 33? That’s 32 more slams he could have entered and wouldn’t be surprising to see him win say 10 minimum. That would have him at least 25 slams (maybe even 30?), and maybe more than just 1 calendar slam. McEnroe is my all time fave, but I do wonder what would have happened in an alternate universe where Mac decided to stay with soccer.