@Fiero425 , one thing your post clarified in my mind is that, in a way, this is rather simple. Rod Laver was the GOAT at the time he played. He was better than his best contemporary, Ken Rosewall, and had surpassed Pancho Gonzales, Bill Tilden, and all the other pro greats because of his two calendar year Slams and his overall accomplishments (Laver is also one of only two players, along with Rosewall, who won the "Pro Calendar Slam" of three pro slams).
And then we have the Open Era. We can say, as you say, that Borg was the first "GOAT" of the Open Era, but we cannot say that he surpassed Laver in terms of accomplishments. Plus, he is problematic because McEnroe, for a short time, was beating him left and right. And then Sampras took the crown, and then Federer, and then Nadal and Djokovic joined the party.
So my point is, Rod Laver is the GOAT of tennis up through the transition to the Open Era and its first few years. He mastered the amateur, pro, and Open Era tours in a way that no other player did.
And then we have the shifting occurring during the Open Era, which has culminated so far with the "Holy Trinity," who are the "crowning" of men's tennis over the last half century.
So I think when we're talking about the GOAT, we're talking about four players that must be mentioned, the first who was the GOAT of tennis up through the transition of the Open Era--about 90 years--and then the trio of Federer, Nadal and Djokovic who have surpassed everyone since. That answer, while not giving anyone singular bragging rights, is satisfying to me.
If nothing else, I feel comfortable placing those four above everyone else, as the "Big Four" of tennis history. The next four, the "Second Quartet," is a bit trickier, but would definitely include Bill Tilden and Pancho Gonzales, probably Ken Rosewall and Pete Sampras.