The fact that Djokovic dominated 2011 doesn't mean that he should get virtual walkovers in 2015 and beyond. 2006 Federer is getting flak for a reason because (and I admit this) - his opposition wasn't nearly as strong as in 2004, 2005 or 2007. Safin got injured, Agassi retired, Hewitt played a lot worse, Roddick started pushing the ball. The same way Djokovic's 2015 shouldn't get a free pass.
2012, 2014 and 2015 prove that he was still in his prime in 2011? Federer is just a great player, he can produce the goods in his 30's but his level is a lot lower than in his mid 20's.
As
@metsman said, Federer only brought his truly prime level at the FO and in the indoor season when Djokovic and Nadal were already on vacation mentally. 1 brilliant match that he played against Djokovic at the FO in 2011 doesn't mean that he was in his prime, come on now.