Just to give you an idea of how extraordinary Djoko's perf is and how overrated Fed's dominance has been, I've compiled the
# of wins over top 8 players per season for each of the #1: Djoko, Fed, Nadal. In parenthesis I list the events where they beat more than 1 top 8 player. I ranked the 6 seasons with most wins for each player:
Djokovic:
1- 2015:
28 (AO, IW, Miami, MC, Rome, RG, Beijing, Paris, WTF)
2- 2012:
22 (AO, Miami, Rome, RG, USO, Shanghai, WTF)
3- 2011:
20 (AO, Dubai, IW, Madrid, Rome, Canada, USO)
4- 2013:
19 (AO, Dubai, W, Paris, WTF)
5- 2016:
16 (Doha, AO, Miami, Madrid, Rome, RG, Canada)- partial tally : Doha to Canada only
6- 2014:
14 (Miami, Rome, Paris, WTF)
Federer:
1- 2004:
15 (AO, Hamburg, USO, WTF)
2- 2006:
15 (USO, WTF)
3- 2010:
14 (AO, Canada, Shanghai, WTF)
4- 2007:
13 (AO, USO, WTF)
5- 2014:
13 (Dubai, Cincy, WTF)
6- 2015:
13 (Cincy, WTF)
Nadal:
1- 2013:
21 (IW, Rome, RG, Cincy, WTF)
2- 2009:
13 (AO, IW, MC, Madrid, Rome)
3- 2008:
13 (MC, Hamburg, RG, Queen's)
4- 2011:
13 (Miami, MC, RG)
5- 2012:
11 (AO, Barcelona, Rome, RG)
6- 2007:
11 (Rome, RG, WTF)
What does it mean?
- that in the year that was marketed to us as the best season ever ( 2006), Fed beat fewer top 8 players than Djoko did in about half the 2016 season!!!!!!!! It also means that in 2006, Fed had to defeat several top 8 in only 2 events!!!!!! 2!!! How ridiculous is that? In half the 2016 season, Djoko had to do that in already 7 events!!!! (so for most of his titles in 2006, Fed beat either 1 or 0) Hello!!!!!!!!!!!!!! How one discovers that the 2006 GOAT season was actually manufactured out of weakness of field and puff draws. The maximum events in a season where Fed has beaten several top 8 is 4!!! In 2015, Djoko beat several top 8 in 9 events! 9! That's more than twice as many as ANY Fed season

And how about 2005? 2005 doesn't even make the Fed list. Fed had fewer wins vs top 8 in 2005 than he did in 2014 and 2015. Talk about weak era and lack of consistent competition at the top!
Nadal had more wins over top 8 in 2013 than Fed ever had in a single season but Nadal's 2010 didn't make the list either, lots of weak draws that year. Fun facts: in 2008, Rafa had more top opponents to beat in Queen's than at W! Last time Rafa beat a top 8 at W was 2011 and it was... title holder Murray. Surprisingly, Rafa beat only 4 top 8 in 2005, his breakthrough year. He won a lot of titles that year but not all big ones and some of the big ones vs lesser opponents.
The first top 8 Nadal defeated in his career was Albert Costa ranked 7 in (where else?) MC. Nadal was only 16 (2003)
Fed's 1st top 8 win was in Marseille (indoor): Moya #5. Fed was 17 (1999). Djoko was a late bloomer, had to wait until W 2006 (19 years old) for his first: Robredo #8. How peculiar that his first big win happened on grass! Now if anyone has a theory as to why all of them had their first big win over Spaniards (rather than... French for instance

), I'd be curious to read it.
ETA: in 2016, Djoko has had 16 wins over top 8, Murray 9, Nadal 4 and Fed 1 (Fed's lone win was vs Berdych- who else

)
ETA2: notice that Fed's 1st top 8 win happened in a 250, Nadal's in a master and Djoko's in a slam.
ETA3: Djoko beat 3 top 8 in 11 events (AO 2011, 2012, 2013, 2015, 2016, Rome 2011, 2015, Canada 2007 (the legendary 1, 2, 3 combo), Paris 2013, 2015, WTF 2008) and more than 3 in WTF 2012, 2013, 2014 and 2015. Fed - insanely- did it only in 4 events!!! (Madrid 2009, 2012, USO 2004, 2007). He beat more than 3 in 8 WTF: 2003,2004, 2006, 2007, 2010, 2011, 2014, 2015. Nadal did it in 9 events (IW 2009, 2013, MC 2008, Rome 2007, 2012, 2013, RG 2011, 2014, WTF 2015) and more than 3 in WTF 2010 and 2013.