Yeah but Boris Diaw has tremendous body control, I'm not gonna call him athletic for NBA standards because of it though, he's mobile. There's also MANY players who are much better at controlling their body on one end of the court, so I'm not sure if its really the '#1 trait'. However I'd argue that it's probably something the Jazz are looking for, because they've said so in regards to Trey Lyles.
In the NBA you have your freak athletes, like Andre Drummond, then there's an elite, or near elite tier just below, and that's where Favors is and will likely remain for some time(whether you qualify the list by size or position). If Favors were to take another leap athletically as this thread asks - where would that put him?? Near Blake Griffin, or Prime Amare?? He's not that type of freak athlete.. especially not at 262lbs.
You can go back and check the Favors highlights from HS or College, when he was closer to a standard sized NBA PF (245lbs) and you will see him with slightly more bounce, I can remember someone using the term "Ultra-athletic" to describe his game.
Lets not forget that Favors was drafted ahead of arguably the best C in the league, DeMarcus Cousins, and surely the reason that took place is because Favors was/is more athletic.