I don't like this "if" and "but" stuff. Many great players including today(Fed/Nole/Nadal) have lost some tough matches which you can argue that they could have won more. And at the expense of the players(who actually won the slam) is minimizing their wins.
I know some of the losses are tough to swallow, like when Fed fans have to deal with Fed losing to Safin in 05 AO after having a match point. But that's part of sport. Some players have to deal with tougher losses than the others, I can agree, but that's not going gain them anymore credit than they actually deserve.
Tier1(goat): Federer; Tier 1.5: Laver, Gonzales, Sampras, Nadal, Borg;
Tier 2: Lendl, Connors, Rosewall, Tilden; Tier 2.5: McEnroe, Agassi