Originally Posted by TMF
Splitting the field does make a huge impact, regardless if you one field had most of the best player like Fed/Nole/Nadal playing in the same field. There wouldn't be a Rosol upsetting Nadal at Wimbledon, no Safin beating Fed in 05 AO, no Nalbandian beating Fed at the Master Cup, no Del Potro beating Fed at 09 USO, no young Fed beat Sampras in 01 Wimbledon, or no Krajicek beating Sampras in 96 Wimbledon. The list goes on endlessly.
And with Roddick in another field who don't have to face these guys especially Federer, he would have a legendary career.
As TheFifthSet pointed out, the big Four have won 31 of the last 32 majors. That's an extreme case but it shows just how much a small group of players can lock up the majors, even when facing full fields.
Your list of upsets is relevant but there is no way to know whether the upset players would have won those majors, if they had won those matches. If Sampras had not faced Krajicek, I think he probably would have won the event. Nadal if he had not faced Rosol, I'm not sure.
Federer, if he had not faced Del Potro in the USO final, would have faced Nadal whom Delpo beat in the semis; and at that time I think Federer would have beaten Nadal; but the principle there is still true, he could have lost.
It's complicated because, yeah, in an open field, Laver might get upset in an early round. But then again one of his big rivals who's been beating him might be the one to get upset (like Nadal was eliminated by Soderling), clearing his way to the title.
I'm not saying you're wrong, I just think that if you imagine open fields for Laver, his major haul might be lower, or the same, or even higher than it actually is. I'm sure you're wondering how it might be higher, but the reason is that in an open field Laver would have 4 chances every year to win majors. In reality he won a lot of his majors with only 3 chances per year (from 1963-67).