Yes, because defense is reactionary. Offensive moves are things that are timed to precision.
Um, defensive moves (blocks, steals, boxing out, even just staying in front of your man) need to be timed to precision; the key difference is that they are not as planned. IMHO, NBA players don't like to play defense because it tends to have less glory tied to it--and because it's probably harder work; Jefferson is no exception.
But I continue to be puzzled how you would think that AJ's defense is due to being slow footed (when your philosophical retort really didn't address the notion that running offenses "to precision" would also require some agility).
From bleacherrreport:
[Jefferson's] defensive awareness is at the very bottom of the chopping block. While he can block some shots one-on-one,
he's horrible on rotations and defensive reaction.
https://bleacherreport.com/articles/419847-the-good-and-the-bad-al-jefferson-traded-to-the-utah-jazz
While the author confirms your claim that reaction is part of defense (something that I was not disputing), his assessment is more akin to focus and discipline, not quickness of step. While Jefferson is no gazelle, the bigger problem is the effort and focus on defense (and maybe the mental skill of D), not the agility.
From NBC Sports:
Jefferson can block shots, but he’s extremely slow-moving on defense,
doesn’t expend much energy on that end, and has long been considered a defensive liability.
https://probasketballtalk.nbcsports.com/2011/01/26/its-time-to-talk-about-al-jeffersons-defense/
Here, John Krolik does mention slowness but leaves it to interpretation as to whether that "slow-moving" is by choice or by chance. His subsequent comment ("doesn't expend much energy") still suggests that the the problem (including AJ's slowness) is due to lack of effort.
From Tim Kawakami, beat writer for the Warriors, who "awarded" AJ a spot on his No-Defense Team in 2008:
It’s clear Jefferson saves his energy for offense–Minnesota was a much, much better defensive team when Jefferson was out of the game. Given Jefferson’s offensive skills, he could become a superstar
if he just tried a little harder on defense https://blogs.mercurynews.com/kawak...-team-starring-nash-carmelo-and-al-jefferson/
Kawakami makes no mention of speed or agility and attributed Jefferson's poor defense primarily to effort ("energy").
But these sources aren't necessary. You might want to check your television or computer screen for distortion, because it was clear on my screen that the core of AJ's defensive weakness is effort and focus (and maybe skill), not agility. While Jefferson has clearly improved offensively, I haven't seen the same progress on the less glory-laden defensive side.
Consistent with the treatment of other big-man cornerstones in recent times, Sloan (and his successor) didn't enforce the D. With even more frontcourt options than before, it's time to do so. A 20/10 player isn't as valuable if he's giving up points on the other end.