Comparisons with other sports are just silly, especially team sports. People who simply watch tennis on tv and/or just play it recreationally have no idea how physical the sport has become. About 4 years ago, Federer himself said he could no longer win simply using superior shotmaking ability, i.e. athleticism, physicality, power, neutralize (to some extent) pure technical skills. And just recently, someone who retired just 2 years ago (can't recall exactly but I believe it was Safin) said he doubted he could keep up with the physicality of the game today, granted he was never the hardest worker.
As an example, last Monday, I played on a court right next to Eugenie Bouchard (top junior) and her coach. Two hours of drill after drill after drill with only a few short pauses. It was grueling stuff. And that was just the afternoon session... Add morning session, physical training in the gym, massage, physio plus the travelling, matches, etc... and it's a hell of a grind just to try and make it as a pro because the level of competition internationally has never been this high.
As I said, 20-30 years ago you could get by in tennis by simply being technically sound and getting fit just by playing tennis (except for guys like Lendl who was a gym freak). That's no longer the case. Tennis now is more physical and demanding than it ever was. Ask Andy Murray if training with former track star Michael Johnson is a "joke"... That's just pure ignorance.