First of all, Federer has the most slams of all time, the most weeks at number one of all time, the most consecutive weeks at number one of all time.
Second, Federer played aggressive, talented, shotmaking tennis. Not grinding/pushing like Nadal and Djokovic.
Third, Federer's era was much stronger. He had to deal with Nadal, Roddick, Agassi, Davydenko, Nalbandian, and had to dance through minefields of talented aggressive players and grass players.
Nadal's comparisons don't even compare to Fed's. He has only had two "great" years and also happens to be a blood doper. Further, 9 of Nadal's 14 slams came from one freaking tournament.
Djokovic is a weak era mug. He has zero competition. You think this is an insane era? LOL yeah, insanely bad. Grandpa, broken back Federer is still making slam finals and is still top 3 in the world. The current era is all MUGS. Nadal is old and washed up as well. Murray is a useless pusher.
Your peak Djokovic just got ass rammed by Sam fucking Querrey at Wimbledon.
You are honestly fucking stupid if you think that tennis is in a "strong" era right now. Federer of 2006 would die laughing at this era and clean up every tournament without breaking a sweat.
As for Fed's head to head with Nadal, it's not really an important stat. First of all, it's a bad matchup. Tennis is a matchup sport. Nadal is a fucking robot programmed just to beat Roger Federer. Secondly, the head to head would be even if they played on grass as many times as they played on clay. Look it up. It's not Federer's fault that a) there are not many FAST surfaces anymore, b) that the ATP slowed down all courts and homogenized them, and c) that Nadal was not good enough to meet Federer on faster courts. Federer was going deeper at clay events, thus meeting Nadal in finals, while Nadal was getting knocked out at other events so HE NEVER FACED PEAK FED OFTEN ON ANYTHING OTHER THAN CLAY.
I guarantee you are a casual