Isn't that what we are talking about? In 2004 he performed at the same level (against non big 4) as in 2011 but still he managed to win 3 GS because there was no big 4 to compete with for GS titles. The theories that he declined overall get busted with this logic.
Okay, so why not use the same reasoning for Nadal?
Number of non-big-4 losses for Nadal in...
2008: 8
2010: 7
2017: 7
Does that mean Nadal hasn't declined from 2008/2010 and was playing at the same level in 2017 as he was in 2008/2010?
In 2003-2007 (5 yrs period) he lost 31 times to non big 4 players but still won 12 GS. From 2008-2012 he lost 33 times to non big 4 but won only 5 GS.
2003 wasn't even a prime year for Federer and there was no big 4 in 2003. I would concede that Federer was better in 2008 and 2009 than he was in 2003. We're comparing Federer in 2004-2007 to Federer in 2008-2011. Your agenda is confusing you.
Federer's prime years are 2004-2007. He lost almost twice as many matches in 2008-2011 as he did in 2004-2007 against non-big-4 players. So, by your own metric, Federer declined from 2004-2007 in 2008-2011.
I don't claim to be very bright but there are different ways at looking the same data and you should not be condescending towards someone who is looking at numbers from different angle than yours.
Point remains that even after 2007 there were many years where he performed at the same level against rest of the fields and thats why these theories of general decline are bogus.
You're not looking at numbers from a different angle. You are blatantly misrepresenting the numbers. Again, here is what the numbers are:
14 losses in 2004-2007.
27 losses in 2008-2011.
So, even by your own metric, Federer performed much worse in 2008-2011 than he did in 2004-2007. There is no arguing against it.