Your point #1 is a something I thought about, and I think that most are in agreement that players like Federer, Nadal and Djokovic are a cut above the rest not only now, but would have been in almost all generations, bar very few. However distance between them and the current chasers is not the issue here. The issue is the competition between themselves, and, moreover, one of players from virtually the same age, mileage, experience etc. The argument that they are the best compared to all the others does't quite apply between those two, or at least it shouldn't, going by their overall resumes.
Your point #2 is more in the direction of what I was thinking. What you say is fundamentally true, players will always have a career that is reminiscent of a bell curve (including such on their preferred surfaces which might or might not be overlapping with the general trend). I can also accept that the best players on the surface can hold their career form better than all the rest in decline. What is shocking to me (and I am saying this without exaggeration) is that the difference between Nadal and Djokovic is so pronounced. I understand that they hold actual advantages over the other on their respective favourite surfaces (as in parts of their game that give them decisive advantages to win over the other: I have always held the view, that mental strength is simply an extension of the knowledge of the player that he holds such advantages vs a particular opponent in particular circumstances, if he himself executes well. Something that is referred to as "the match being on his racquet")),
but we are witnessing literal destructions of the other. Something that shouldn't be happening, if those players are all they are described to be (ultimate fighters, well rounded games with no obvious weaknesses, tactically astute, physically on the highest possible level etc). Something doesn't quite add up.
Additionally, they are reaching the latest stages of the tournaments, and think about it: when Connors lost to McEnroe in the 1984 USO he didn't go down on a straight set trouncing, despite of being already 32. He lost to a player that convincingly trashed the other player in the finals. Rosewall did very well everywhere in old age, I am not sure what the thinking is behind mentioning his name in that regard. He beat 8 years younger Newk for his USO F qualification in 1974, and USO was hardly his best tournament (although, to be fair, it is hard to say which was his weakest, he was that good).
To your third point: it appears that in that frame of thinking we have more a case of establishing that such disparities indicate that those players have not been the level of competition that was originally thought
in the first place. Their steep decline on their "weaker" (or is it weakest?) surface/conditions/whatever, to the point of not being able to hold even a
respectable level of competition against the other competitor, despite of being held in highest regard on multiple points as far as tennis ability goes, indicate that the few times of them going toe to toe has created the wrong impression of that rivalry.