It is not snobbery. No one is discrediting Nadal, and I guess that everyone accepts that he is the best tennis player of all time in clay surfaces, and very likely the most dominant tennis player in a grand slam.
But, I think that context matters and in GOAT debates, it is good to see how well players did outside of their comfort zone. Taking Nadal outside of his preferred GS, he has won 5 grand slams which is still quite good. Taking Federer outside of Wimbledon, he has won 11 grand slams which would make him joint fifth most successful (male) tennis player. Nadal would be just joint 28th. In addition, outside of his preferred grand slam, Federer has won 5 grand slams in each of US Open and Australian Open. In each of them, he has won as much as Nadal did in three GS that aren't French Open.
Essentially, Federer is the greatest ever, with Nadal being the greatest in clay surfaces. Also, he has been a more dominant player in clay than Federer in grass, which would make him the most dominant player in a unique surface. But to be the greatest ever, you need to do great in more than one type of surface.
The vast majority of people put Nadal in second or third place. Which is hardly diminishing his results or a snobbery.
On comfort zone, though Grass is preferred surface for Federer, it was never a big difference for him to play at hard courts. He started winning and dominating at Australian open and US open around same time as Wimbledon. So, outside the 'preferred surface slams' don't mean much at least in way you have put up. Federer was never thought to be one surface player. His win % at Wimbledon is 88% and it is 87% at AO and US open. Not much difference. About Nadal it was different. People had doubts about his ability on other surfaces initially.
About the argument people put about 'peak Federer', again it is something I don't agree with it. It is just a qualitative aspect introduced by Fed fans to show that the reason Federer started losing to Nadal and Djokovic is because he was past his peak. I am hearing it since 2008-09 when he lost to Nadal at Wimbledon and then in 2009 at AO. He was just 27-28 then! 27-28 is not past peak especially when player is around still, at age of 36. His playing style is not Djokovic-Nadal like and he didn't have injury problems of Nadal. The Federer beating Baghdatis and Gonzalez and Roddick million times is not necessarily a 'peak Federer' who was at even higher level. He looked at higher level due to such average opposition. Djokovic and Nadal have a very good counter for Fed style and he took long to adjust to it. If those 3 had played at same time and if Nadal didn't have so many injuries, I will put Nadal as favourite to win most, followed by Djokovic and then Federer. Including Nadal's injury situation, the position of Nadal-Djokovic changes for me, Federer still 3rd. Mind you, I am not discrediting or downplaying Federer. Probably the count will remain too close, differentiated by slam or two. I am basing it on the fact that Federer had to adjust his game to counter these two and still had limited success at biggest stage so it depends in hypothetical scenario of peaking at same time, how soon he adjusts.
It is all ifs and buts though and Federer could only beat what was in front of him before these 2 and few other quality players came through. Yes he was on slightly downward curve when these guys were approaching peak but he wasn't totally past it and it wasn't as if his peak was something so different where these guys won't have stood chance.
Most of Djokovic-Nadal slams have been against either each other or Federer or Murray in finals and en route some more quality players. Federer had quite a few freebies earlier and there was gulf in class between him and others. Only player who could stand to him was Safin but he had too many other issues to be consistent.
Still all said and done, for now, I can put Federer at top, slightly, just because 18 is 18 and that his 18th is his greatest of all. Just want to make clear to Federer fans though that it is not as clearcut 'GOAT' as they like to make it out and Nadal and even Djokovic are not done yet. If somehow the count becomes 18-16 with Nadal, it won't seem that straightforward. I won't put it past Djokovic of winning 3 more too. He is bit burnt out, maybe has some other issues, but he will come back. He can play 2-3 more years I feel.