You forget this is not about Nadal being superior to Federer at this point. Nobody is seriously arguing that unless Nadal gets very close to Federer in slam count, which he is a long way from being right now. This about the fact Federer is legitimately owned by the 2nd best player of his own generation. Something that is not even close to true of any other GOAT candidate, and certainly not of Sampras.
Only because Federer has been good enough on his worst surface to get to the finals. Your logic is idiotic and fails. By that logic, Federer would have done "better" to fail to reach all those FO finals. Sampras would have been clobbered by a number of clay-court specialists had he done better at the FO. He might not have had losing records vs. any of them anyways, but that just shows how stupid the H2H argument is.
According to the H2H "argument", it is better to lose early than to get to the better opponents, or it is better to distribute your losing equally among 3 players rather than all to 1. Reality is, not winning 4 FO titles is just as bad whether it is because of 1 player (Nadal) or a variety of players (as in Sampras' case). And getting to the FO final is better than not getting there.
How about this argument: Sampras was lucky to never have a rival as consistent and great as Federer's rival Nadal has been?
I'm not interested in debating whether Federer or Sampras is the greater player (although the arguments in favor of Federer are obvious and aren't fallacies, like your arguments). However, I will say that you can't use Sampras' failure to get to the FO finals even a single time as an argument that he's better than Federer; you can't use Federer getting to so many finals as an argument against him. And to use the H2H as some kind of argument against him as a GOAT candidate is ridiculous because tennis is not about H2H's: it is about winning championships and being ranked #1. The "H2H" vs. the field at important events in a player's prime would be more important...and there hasn't been a player in history who has dominated tennis as thoroughly on that basis in terms of winning %, events won, & GS won...except for Laver. Sampras never had a 3-slam year, and his best years in terms of slams & win % were
maybe on par with Federer's 2009 year.
You seem to think that Sampras is under-rated because most now consider Federer a greater player. That hardly constitutes him being "under-rated". Nor is Federer under-rated by those who consider Sampras a greater player. It is debatable. I'll say is H2H isn't a particularly relevant criteria (b/c of idiotic results coming from it, like it being better to lose early, or like it being better to lose 9 times to 3 different players than 9 times to 1 player, in failing to win a tournament, when both are just as bad). No one who brings up the H2H argument has ever (nor will they ever) had a satisfactory answer to the double-counting going on when you look at H2H & GS wins & ranking, nor any of the other idiocies resulting from H2H arguments.
Sorry, but Sampras is not "insanely underrated". Only a delusional **** would say that. He is considered by almost
everyone to be an all-time first-tier great, a clear candidate for GOAT, even if most think Federer and Laver are above him there. I rank Sampras as the 3rd best & greatest player of all time (in the Open Era), and I think the worst just about anyone could rank him would be 4th if you put Borg over him. Because Laver won the GS, I can't rank Federer over him and consider it a tie for 1st. Borg I put at 4th, and Nadal may very well join him or even bump him down a notch.
Btw, if someone ranked Sampras & Borg above Federer, I wouldn't say that person is "insanely underrating" Federer. Both did things that Federer hasn't and won't before his career is over (6 yr-end #1 & the repeated Wimby-FO doubles), and that's their subjective evaluation. If someone were to say Federer isn't a 1st-tier all time great, I'd say that's insanely underrating him.