Another note : I don't like when too much focus is made on "this player didn't win that tournament" ... although it was clear from everything he did in that period that it was really a mater of bad luck that he didn't achieve that because he had everything to do it.
People should be flexible and "expert" enough to realize those things imo.
Two examples :
- the constant "Borg didn't win the US Open" argument : some people defended him already then I will not insist, but clearly this argument is too much used, esp. in the comparison with Nadal (on the other side, Borg is clearly disadvantaged by the little importance given to indoor tennis in these rankings)
- the argument "Becker was a mug on clay because he didn't win a MAsters 1000 on clay (contrary to Edberg and Sampras) and didn't reach the FO final (contrary to Edberg)" : I mean people who watched tennis in the end of the 80s and beginning of the 90s know that it was really a matter of bad luck and no Becker overall was a better claycourt player than Edberg and Sampras. He played 5 Masters 1000 finals on clay (Edberg 1) and 3 French Open semifinals (Edberg 1) !! He lost 8-6 in the final set the Monte-Carlo final 1995 to the clay beast which Tomas Muster was in that time ! Against Mancini in 1989 it was very tight. In Roland-Garros some people here said that if he had defeated Edberg in 1989 (and it was very very tight), he probably would have defeated Chang in the final, who was a good match-up for him ! And then what ? a few points more and Becker would have been a clay king ? that's bullshit : Becker was the same winning or not those few points, I don't accept the manichean arguments "it's black or white, not grey".
Still comparison mainly must be based on figures. Because you can go too far from reality. Personally I think that Rios, for example, was underachiever because of bad luck, he had everything to win all the Majors apart from Wimbledon for a few times and be at least in TOP-30 here.
On this level of historical "competition" one-two points > one-two wins > one-two titles decide almost everything in grading, IMO. A lot of players are extremely close.