Watch the tape of his matches. He's (Borg) is pretty clearly
NOT one of the best movers to play by contemporary standards. He's giving up on balls hit wide that are almost rally shots today for great movers like Novak, Nadal, Medvedev, etc.... He's an all time great, but insisting he's comparable to Novak is like comparing NBA legend of the 1950's Bob Cousy to Steph Curry. Novak is 3-4" taller, probably has 6-7"+ reach advantage, and is objectively faster/quicker across the court. As the song goes, "One of these things is not like the other"
Borg actually ran a 12.3 100M dash (per
The Superstars database). Only people whom don't know about track speed (even if you didn't know he ran a 12.3 100m) would suggest Borg was anywhere in the same galaxy as an Olympic Level sprinter. Outside of just a few skill players in the NFL with track backgrounds, there really aren't
true world class sprinters (ie. athletes whom have run those times in competition) playing other sports professionally anywhere in the world.
I don't know if your slow or stubborn here as this is not a difficult concept. Players have done all kinds of things in isolation as you note, but Novak moves and plays defense/transition in a way that was unlike anyone who came before. It just is.