I like Becker as well, but let’s be honest, he was always beatable. And do you really think peak Federer would have lost to him even in RR matches or have a 40-15 situation? On the other hand Sampras never had to play against Djokovic of course. By the way, contrary to your suggestion Agassi has a slightly better H2H percentage wise against Becker (9-5) than Sampras (12-7).
To Sampras himself: He may have a winning H2H record against most of the important players of his era (not all, see Krajicek, Stich and later Hewitt, Safin etc. when he really wasn’t THAT old). But his problem was that just like Becker he literally could lose to anyone on any day when one aspect of his game wasn’t working. Okay, let’s say this was the case apart from Wimbledon. Look at the names he lost to at Slams from 1997-2002 and don’t say me Federer would have lost to anyone of them during the same age.
But by the way, that are only arguments why Sampras wasn’t GOAT. Other than that I was his fan and loved watching him play.
Firstly, Agassi lost some pretty important matches to Boris, contrary to Pete who won them all, unless you consider the Stuggart final an important one. Agassi also admitted in his bio he lost to Chang on purpose at AO so he wouldn't have to play Boris.
And when Boris was on, he was as close to unbeatable as it gets. With the sole exception being Pete.
He would have all the tools to beat Fed: mentally strong when on, as (or even more) powerfull as Nadal , a total player like Fed, a slightly better server.
If Henman with his net play and touch could dominate Fed for long periods, you think Boris wouldn't have found a way ?
After getting beat by both Edberg and Stich in the W finals, he made sure to further dominate both. He never again lost to Edberg.
As far as Sampras having surprise defeats, people conveniently forget he managed to dominate everybody while having thalassemia minor. Hence his poor record on clay.
When you have such weapons as one of the best serve ever, nerves of steel, sublime touch and netplay and powerfull forehand, there aren't too many people able to beat you.
Krajicek managed it one year playing lights out tennis, but he was a beast. Fed doesn't have the power to blast through Pete like him. And once the ball got into play, Pete could win from any part of the court.