Fabio Fognini competed against all the members of the big three and he knows that Djokovic is likely the strongest one tennis-wise but also the least popular.
It's not a secret that Djokovic faced the impossible task of converting tennis fans from Nadal and Federer to himself when he arrived on the professional scene. Tennis had this perfect rivalry between two respectful players whom everybody loved and everything was so perfect. In many people's eyes, Djokovic came and ruined everything by inserting himself into the story.
It made it almost impossible for him to make yet he did in spite of everything. For Fognini, Djokovic is the strongest one when speaking about pure tennis albeit also the least popular one:
"Nole is the strongest and the numbers prove it, but he is
also the least loved of the big 3. It is difficult to find a suitable
adjective for him. Last year he did not play two Slams and four Masters
1000, but still managed to qualify for the ATP Finals."
Fognini also praised the way he returned and won Australia after last year:
"After everything that happened last year in Melbourne, Nole came back and made his mark. He, Roger and Rafa monopolized the circuit and wrote the history of this sport."