I am unable to respond to your quotes within my quotes.
On the AO, I agree that Nadal is as tough to Fed as Agassi was to Sampras. In both cases, the score was similar: 2-0 to Agassi and 2-0 to Nadal.
At the USO, Fed never played Nadal while Agassi played Sampras 4 times. So I think Agassi was clearly a tougher opponent here. Agree about clay/grass.
My main point was that even the Fed-Nadal rivalry should've been dictated by the surface, just like the Agassi-Sampras one. Fed is, technically, a better grass court and HC player, and clay is the only surface that Nadal is clearly superior on. Part of the reason why Nadal creates issues for Fed even off clay is because Fed plays him like he does on clay.
And this brings me to the "match-up" - Nadal's FH CC to Fed's BH. Theoretically, this is a difficult shot to handle for a 1HBH. But, outside of clay, I think this is something that Fed is significantly to blame for allowing Nadal to be able to set that particular template. It's curious how Nadal didn't "allow" for the reverse - Fed's FH CC to Nadal's BH. Nadal's BH is more consistent than Fed's BH, but, surely, Fed's FH is stronger than Nadal's BH, right ? Further, Agassi had that advantage over Sampras too. It's instructive to see how Sampras didn't allow Agassi (or any other baseliner from his era with a 2HBH) to totally use that strategy against him on the faster surfaces. It always takes two to tango, and so Nadal being able to set the template/pattern for Fed is partly with Fed's "cooperation".
Now, this also brings me to the "technical/mental" part of Fed's game and why it plays to Nadal's hands. Fed is a Tier 1 "jack-of-all-trades" player. IOW, Fed is excellent/great in many aspects of the game without being an all-time great in all of them. For example, Fed has an excellent serve, but he's not in the same bracket as Sampras/Ivanisevic/Krajicek/Scud/Stich in terms of the serve being consistently big, game-in and game-out. He's ok doing it here and there through a match, but he cannot do it game after game like those guys used to do. Fed has great power in his shots, but he doesn't pack as much power/punch as those guys because he puts more spin and puts a little bit more emphasis on consistency. Fed has great defensive skills, but he's not as good as Nadal/Djok in that regard.
So what are the implications of this ?
Basically, when two really talented, great players play, on most neutral surfaces, the player who has
fewer shots/options in his repertoire (obviously, this is relative to each other and not in an absolute sense, for all pros are really, really good in all the strokes in tennis in an absolute/stand-alone sense), but is an
all-time great in those few aspects, tends to have an advantage over the player who is excellent in all aspects but is not really an
all-time great in enough of them.
So, when Fed plays Nadal, he is in a quandary. He can serve Nadal off the court for a few games, but that is only sporadic. He cannot do it most, if not all, of the times; he can punch through Nadal for a few games with his groundies by hitting flatter and closer to the lines, but he cannot do it for prolonged periods; he can come to the net, play S/V etc. for a few games/points, but cannot play the entire match that way. So there is no
go-to pattern for him. This also creates a problem on the big points when Nadal is that little bit extra-keen, because Fed is confused (and lacks confidence) about what shot to play: "Should I go for the ace ? Hmm, I'm not that confident that I can land it bang on the line at 125 mph. Should I play S/V ? Hmm, not that sure about that either as it's not my main game. What if my volley sits up for a pass ? Should I hit by BH/FH DTL ? Hmm, a risky shot and not totally an advantage unless I follow it to the net".
Also, this is why I disagree about the surfaces being disadvantageous to him vs. the field. Only Nadal (and later, Djok) were good enough to push him into this situation on these surfaces. If the surfaces were faster and lower bouncing (grass at Wim too) like in the 90's, guys like Blake, Roddick, Ljubicic, Berdych, Tsonga, Soda etc. would've been able to hit through him a little more easily because Fed wouldn't be able to set up as easily as on the more slower surfaces during his time. They would get a few more aces in their service games etc.
Also, I think a lot is being made of Fed's display against Sampras. For one thing, it was just one match and a close one. Think of this one: what if the only sample we had to analyze was the Berdych-Fed Wim match of 2010 or the Tsonga-Fed Wim match of 2011 ? What if we drew conclusions from that match ? One match is not enough of an indicator. Further, I'm not convinced about Fed's ability/propensity to play pure S/V. Keep in mind that both Borg/Lendl played far more S/V at Wim than Fed ever did. Watch Lendl beating Edberg in the 1987 Wim SF playing S/V, or Lendl demolishing Becker in the 1990 Queens Club playing full blown S/V. And yet, nobody ever thought that they
could've been S/V'ers like Mac/Becker/Edberg/Sampras. More proof of this is that Fed NEVER played like that outside of grass (watch his USO match in that same yr, 2001, vs. Agassi).
Fed's mentality is not of a S/Ver either. S/V'ers are not scared of being passed by a baseliner. They expect it, accept it, as part of the bigger picture. They don't mind being passed 49/100 times as long as they can hit winning volleys the remaining 51 times. Fed doesn't seem like that. Once Nadal passes him a couple of times, Fed abandons the S/V tactic. It's clear that he doesn't like the feeling of being passed, the feeling of being at the mercy of his opponent sometimes.
Fed's volleying is technically flawed too on the FH side. He doesn't bend his knees quite as much as he should. He also tends to reach for the ball instead of getting to it with his feet. This results in his elbow being farther out from his body, and the racquet head dropping lower than the wrist. And this also results in him not getting enough "punch" in his FH volleys, and results in the volley spooning up. His "swing volley" is another give away of his limitations with the FH volley in that he cannot add power to the FH volley UNLESS he has some pace to work with. So, all in all, I'm not totally convinced of his being able to match guys like Sampras/Becker/Stich/Edberg at the S/V game. Fed is, at heart and technically, a baseliner though he's a little more well-rounded than most other baseliners we've seen. Actually, a much stronger case can be made for Sampras becoming a very good baseliner than can be made for Fed being a S/V'er.