Fed will only improve physically from now on, his back getting stronger with each match. He is just in his first phase of domination clay, he's about to enter the second phase of his career where every win on clay will be in straight sets for Olderer, never being broken. You can expect another 4 Basel titles. He will also start his domination on clay, and by the end of this second phase he will be known as the new clay GOAT. This second phase should start next season and will likely last 50 to 70 years, featuring 30 more titles at both the Luxembourg and Basel and a 6 year being undefeated at Rotterdam. The third phase of his career will last for another 100 years after that, years during which Olderer will only win 6 slam titles a year, but he'll still remain #1 in the rankings based on his record setting 10 straight seasons with 8 Dubai titles. Not counting his 3 additional silver medals.
Don't get the point of this thread. Fed fans don't have much to fear - Nadal's knees have basically killed any chance of passing Federer - needed to win at least 2 slams this year. Trying for 14 is definitely more realistic - couple more RG and maybe a Wimbledon seem do-able if he's playing 2+ more years. All that said Nadal also isn't playing in an era where he has no great rivals - he has only won 1 slam without beating at least 1 of Federer/Murray/Djokovic (French Open 2010 - would have won if he'd faced those guys anyway) - Fed on the other hand had many times where the final itself really wasn't a mental battle - imagine facing Baghdatis or Philppousis in a best of 5 match. Novak, Rafa and even Andy would cruise too.
So yes, Nadal will stay behind on the slams metric and the age metric from now on, but ultimately his slam record will be looked at very favourably when considering his era and opponents. Fed's greater than Nadal but the need for Fed fans to pick reasons why, or try and console themselves that the record will remain, is all a bit much.
For me if Nadal gets to 15 - i.e., second overall - with Fed still at 17 - it'll be close enough to ignite debate. Hope he gets there.