Here's another way of putting it: Being an athlete, even a great athlete, does not make you a scholar - even of your own sport. I bet most of us here know more about tennis history than most players.
As for the notion of the futility of making a list, what if we thought more in terms of tiers or groups of players? Maybe if we were more vague we could, at the same time, be a bit more accurate and firm?
So for example, we could group players as follows:
First Tier - Inner Circle, or GOAT candidates: Tilden, Gonzales, Rosewall, Laver, Sampras, Federer, Nadal, Djokovic
Second Tier - True Greats: Wilding, L Doherty, Budge, Riggs, Connors, Borg, McEnroe, Lendl, Agassi
Third Tier - Lesser Greats: Vines, Perry, Crawford, Parker, Cochet, Borotra, Kramer, Trabert, Sedgman, Segura, Drobny, Hoad, Emerson, Newcombe, Wilander, Edberg, Becker
Fourth Tier - Borderline, or Near-Greats: Fraser, Patty, Santana, Cooper, Ashe, Nastase, Vilas, Courier, Kuerten, Murray
Fifth Tier - Very Good, but not quite Greats: Stolle, Gimeno, Roche, Smith, Orantes, Gerulaitis, Muster, Ivanesivic, Chang, Safin, Hewitt, Roddick, Wawrinka, etc
(This is list is not meant to be exhaustive - just what I could put together in a few minutes)
This opens up questions about which group a player truly belongs in . For instance, does Sampras (and Rafa and Novak) belong with the true inner circle greats? If Rafa and Novak don't, what do they need to accomplish to get there? Is Murray still a near-great or is he now in the "lesser great" group? Etc.