These stats are very misleading because they favor clay courters. Especially clay courters who play Mickey Mouse tournaments and face weak opposition.
For example, Berasategui's stats:
Return Games Won: 25% on hard vs 32% career
First Serve Return Points Won: 28% on hard vs 34% career
Second Serve Return Points Won: 54% on hard vs 58% career
Break Points Converted: 43% on hard vs 45% career
His HC numbers are all worse than Djokovic's, while Djokovic's clay numbers are marginally better than Berasategui's.
Difference is, Berasategui played 77% of his matches on clay. Novak is at 24%
Yeah, I get what you're saying. This is why I was saying you really have to subdivide the return. It isn't a universal stroke. It has a different characteristic depending on the surface.
Agassi and Djokovic on HC are nearly identical. Agassi edging out Djokovic on a couple of things. Djokovic edging Agassi out on a couple of things. The same for the other surfaces.
But check out Connors return statistics on HC from 1991 to 1996 (which is all the ATP has recorded)... compared to Djokovic :
Djokovic Career Return Stats On HC
33% - 1st Serve Return Points Won
55% - 2nd Serve Return Points Won
3,838 - Break Points Opportunities
45% - Break Points Converted
5,473 - Return Games Played
32% - Return Games Won
42% - Return Points Won
54% - Total Points Won
Connors Return Stats On HC from 1991 to 1996
33% - 1st Serve Return Points Won
54% - 2nd Serve Return Points Won
465 - Break Points Opportunities
42% - Break Points Converted
639 - Return Games Played
31% - Return Games Won
41% - Return Points Won
50% - Total Points Won
Given Connors' age (39 to 44) for those stats, the racquet head size he used most of his career, the surface conditions, and the great servers he faced... he simply has to be the greatest ever.