Djokovic has been a consistent force for quite some time, (2007-now) but he has been pushed by several players, on his best surface and on his worst that should be way below par. Lleyton Hewitt, way out of his prime and ranked in the 180s pushed Djokovic at the Australian Open of 2012, winning a set. Later on in the year at the Olympics, had chances at winning the match they played. Wawrinka at this Australian Open this year had many chances of winning their match. Nadal, arguably playing on his worst surface, took Djokovic to 5 sets and was up a break before losing to Djokovic on his best surface. Djokovic is a transitional champion that is benefiting from Federer and Nadal playing into their mid 30s and early 30s and is reaping the rewards by beating lesser players on a surface that can take years to adapt to. This does not diminish his accomplishments, but I am sure many past greats were better in their prime/peak.