I wouldn't call that mindless, just not as cerebral as some tasks. But mindless or not, if it needs to be done then it's still productive work. Why the author feels that only "deep work" counts is beyond me.
If I could turn the first type of work over to an AI assistant so I could spend that time napping or working on a hobby or side interest, that would be cool. But that's not the goal of companies pushing AI. They figure if I don't have to do the "mindless" work anymore, I can do "deep work" for my full 40 hours. But maybe I'm not capable of working more hours at that level of focus. Maybe the hours spent doing "mindless" work are necessary for resting and recharging between the intense sessions. So if my company takes away the "mindless" work, they're probably not going to get the jump in productivity they're going for. They're more likely to burn me out and send me looking for a new job.