my goat is sampras, so i couldn't care less about this current goat debate, i'll leave it to those who enjoy baseline tennis
still, djokovic raised his game for 2011 and is rightfully belongs to the same tier as federer or nadal.
djokovic had to overcome nadal's 16-7 lead (that was the biggest diff between them in '10) and eventually overtook nadal in their h2h at the beginning of 2016. 2010 was easily nadal's best year, and he lost next season's h2h 0-6. we can safely say that djokovic dominated their rivalry since 2011. if you still consider 2016 as the turning point (which actually happened years earlier), then declining nadal still won 6 gs trophies (4 rg's) and spent zero weeks outside of the top10 ever since. (he was in the top3 for most of the time.) not something i'd necessarily call a decline.
the h2h vs federer is different in a lot of ways, but the turning point still was the same 2011 season. djokovic was trailing roger 6-13 by the end of 2010, then won 6 of the next 7 matches between the two. 2011 was the first year when federer couldn't win a gs since he won his first, so you can call it the beginning of the end for him. but the bottom line is that djokovic found his winning formula vs both players in 2011.
my 2 cents on the goat debate: nadal is the undisputed clay goat, but he's not even a top10 ever on any other surface. everything else is debatable. goat will be decided when all 3 retire. if i had to pick one goat for grass, it's between sampras and federer, with borg at 3rd. djokovic for indoor, federer or djokovic for outdoor hard courts. federer and sampras are easy top10 ever players on 2 surfaces, probably only borg compares. serve: sampras or ivanisevic. volley: sampras or rafter. return: djokovic or agassi. weird, unexpected & brilliant shots: santoro.