I'd love to see the numbers on that.
FH speed, foot speed etc.
I think what's happened is the competition caught up and passed him.
Purely subjective on my part.
You can't expect to really maintain your focus for over a decade, keep your motivation 100%, not to mention your movement, speed and reflexes.. They are elite athletes, however, they are still human... Are you going to tell me that you are as fast as you were 23-25.. Put it this way, when I was 23-25 I could easily go out Wednesday, Thursday, Friday and Saturday, get hammered every of those days, wake up with just a bit of a hung over and start drinking and partying again.. At my age I sure as hell can't do that anymore, I go out, drink just a bit and next morning my head is just spinning and I just want to go to sleep or relax in the leaving room... To say that Fed is still intact and exactly with the same quickness, reflexes, motivation and focus than when he was winning 3 Slams a year is just ridiculous... You always lose something along the way, even elite players.
IMHO Fed has improved in some ways, (serve, dropshots, etc.) as well, but he is not the same player than he was in 2004... No that hungry anymore to be the best in the history of tennis... he already is (at least from most TV celebrities, pro players, etc.) he has nothing to prove now, and you are telling me that he still is hungry for titles? I think he is hungrier for publicity, media coverage, than he is of what made him the 16 GS winner.
So, bottom line: Djokovic / Nadal have risen the standards. For sure! specially Djokovic.. they are playing great... But Fed is not the same guy we used to watch several years ago.. And don't get me wrong, I do like this Federer, and I still love to watch him play.. but he doesn't have that same "magic" he once had..
Ask Dallas, I am sure she would agree with me.