Nadal beat Roddick 6-7(6), 6-2, 7-6(6), 6-2, at the 2004 Davis Cup. Nadal was 18 years old at this point, so he was scoring wins over prime Roddick at just 18.
Now hang on about Federer not beating "baby or prime Nadal", he's lost to Federer in 2005 at Miami, although it was an incredibly close match. It's still a win and he still beat Nadal, so that renders that argument null.
He also beat Nadal in 2007 at Hamburg, 2009 in Madrid and this year at Indian Wells. His wins at Wimbledon in 2006 and 2007 count towards the ending tally. Also the fact that Federer has been schooling Nadal at the Tennis Masters Cup every time they've played.
I notice you forgot to mention (probably conveniently) that this match was on clay in spain. Yes Nadal was only 18, but even at that point he was much better than Roddick on clay. I also notice you've mentioned some matches where Federer beat Nadal, but see here's the problem. Nadal was tired at 07 Hamburg and 09 Madrid, the wind was a problem in IW, Nadal was a baby at Wimbledon in 06 and the scheduling was the problem at 07 Wimbledon. And mentioning the TMC is laughable. It's only an exho. It counts for nothing.
As for Sampras's biggest rival, obviously it's Agassi, but it just shows that Federer's had a tougher rival. I've noticed a lot of people like to pump up Sampras's era, but if you take a closer look it's at least no better than Federer's era. Agassi had a late surge in his career, but he was so mentally tough that his ranking dropped to the point where he was playing challengers at 26 years of age because he couldn't handle the mental blow dealt to him by Sampras at the 1995 USO.
Courier couldn't handle Sampras when he hit his prime. Won 4 slams in between 1990 and 1993 before Sampras really hit his prime, and 2 of those on clay where Sampras was well below average anyway. Didn't beat Sampras at the Aussie when Sampras was heartbroken for his coach. That was probably his best chance.
I've also seen people that like to talk about Becker and Edberg. That's fine, but I don't believe Sampras ever had to beat Edberg at any point to win any of his slams. Edberg was past his prime by the time Sampras peaked, as was Becker, although to a slightly lesser extent.
My point is that if you dominate of course it will look like you have no competition, when in fact the more likely idea is that both Sampras and Federer are really really good.