I absolutely agree with what you're saying. I'm
not saying that those things are measures of productivity, or that they're disqualifying. I'm saying, there's
part of a holistic understanding of work ethic... (which is a different thing than productivity). If someone is goofing off occasionally, but delivers their work, that's a
good thing. Having a healthy amount of goofing off is not only not a problem, it's part of a healthy work environment.
But, over my career I have literally seen egregious instances where someone, habitually, up against a deadline shows up to work late, sits down in their cube, puts on a gaming headset and plays an MMORPG for a few hours, then shows up to the standup and says they need more time to get their work done. These situations are something that even the most Theory Y manager would need to address.
Luckily I now work in workplaces where I have the luxury of hiring people with a track record of success, but in places where many hires might not be aware of commonly accepted workplace expectations, these things do happen. That doesn't mean you should treat everyone like children, as you say, but it does mean you need to be aware of your employee's attitudes and expectations.