Borg was absolutely done with tennis after 1981 where he had to take two back to back losses at Wimbledon and the USO. And he was only 26 when he retired. Also played AO only once as it was no where as popular as it is now. Even Sampras skipped it a couple of times as it was still not as popular and Sampras really hated the long flight. So obviously all these past greats skipped a great deal in the past and retired early, so it's really not fair at all to compare them with today's players. And there are so many other things that need to be taken into consideration. Even if you do that, it's just not possible even remotely to compare eras.
Even McEnroe was exhausted due to heavy competition after 1986 at age 27 and was on 6 months sabbatical. Was never the same player after coming back though still won a few titles but never another Slam. And the competition had moved on by then with the new comers like Becker, Sampras, Agassi, Courier, Chang etc.
I really think Borg, McEnore were really talented players ... more so than the likes of Connors, Lendl etc.