Another thought about Borg is how much his retirement impacted tennis in the early 80s.
Let's have a bit of fun and imagine if Borg hadn't retired when he did. To start, let's say he took a breather from the 1981 US Open to the 1982 French Open, but then came back refreshed and ready to play. Maybe he had a spiritual epiphany and realized he loved the game and wasn't ready to fully relinquish his crown to that uncivilized New Worlder.
Chances are the 17-year old Mats Wilander wouldn't have been able to beat Borg at the French Open, so there's one off Maty's record. I'm then wondering if McEnroe would have been more focused and with Borg there, I'm guessing Jimmy Connors wouldn't have won Wimbledon and the US Open - there's two off of his record. Let's say Borg takes the FO and he and McEnroe split Wimbledon and the US Open. This changes total Slam tallies to: Borg 13, McEnroe 8, Connors 6, Wilander 6 (career totals, but through 1982 changes). Its also conceivable that Bjorn could have taken the #1 ranking back.
Moving to 1983, I think we would have seen more of the Borg-McEnroe rivalry, with McEnroe taking back (and probably keeping) the edge. But I still think Borg takes the FO, so Yannick Noah loses his one Slam. Then maybe Borg and McEnroe split Wimbledon and the US Open again. So the tallies go to Borg 15, McEnroe 8, Connors 5, Noah 0.
In 1984, we probably start seeing some slippage from Borg - he's turning 28. Maybe he finally loses the FO, which goes to Lendl. We'll let Johnny Mac keep his two, so Borg goes slamless for the first time since 1973. No change in tally from above.
In 1985, Borg wins one more - defeating Boris Becker at Wimbledon. But McEnroe wins the US Open, so Lendl loses a Slam (remember, we're assuming Mac would have been a bit more focused with Borg still in it). Borg 16, McEnroe 9, Lendl 7.
In 1986 Borg goes slamless again and retires. Johnny Mac also goes slamless, but comes back and wins one more in 1987 - maybe taking Pat Cash's lone Slam at Wimbledon.
So the final tallies in this imaginary scenario would be Borg 16, McEnroe 10, Lendl 7, Wilander 6, Connors 5, Noah 0, Cash 0.
Later on Sampras isn't able to pass Borg, so Federer's #17 is all the more meaningful.
All just a made-up story, but kind of fun to think about!