LOL at you putting Murray at the same level of battling Federer and Djokovic. And that's because Nadal has only 4 slams outside of clay anyway. As if Nadal has any great rivals on clay? The second best claycourter of this era is Federer and clay is Federer's worst surface. Wimbledon 2010, he only had Murray to deal with. And let's not act as if beating pre-2011 Djokovic is the same as beating Djokovic today.
Murray's not the same level as Fed or Novak but talent and game wise he's far superior to Roddick, Baghdatis, Hewitt etc. Sure Andy, Lleyton etc. may have got the slams due to when they played but they never had the complete game that Murray has. Murray showed his game could hurt the top guys from when he first emerged on tour and he's a real rival to the rest of the top 4 even if he hasn't won a slam yet.
Anyway, Fed has 17, Nadal 11. Not even comparable yet. My point was that somehow focusing on Fed doing better age wise now is stupid - it was always expected Nadal would do better when younger and given how many slams he's missed he's not done too shabbily. I don't think Fed played in a "weak era" - he was always going to be too good. But I do think post 2008 as Novak and Murray stepped up the competition at SF, F level has been tougher for all for them and that will be count in Nadal (and Fed's for his later slams) favour.
At this stage, it's irrelevant. 6 is too big a gap. If the gap becomes 1 or 2 slams then I'm sure other factors will be considered. Fed has many more arguments than just slam numbers of course but it would allow for a debate where right now I think the slam difference is too big to entertain it. Finally, weak clay era is a stupid argument. Anyone can see just by watching Nadal's game that he would have been just as great in any clay era. Fed is a fantastic claycourter and has squeaked out 2 wins over his career. Same for Novak. Coria was great and struggled. Ferrer's pretty great and will run all day but still struggles. Doubt Guga would have denied Rafa many titles.