Employee C: I'm leaving, see you tomorrow!

As your co-worker or your boss, why do I care in the slightest whether you're going home to take care of your kid, to smoke a bowl and watch a movie, or because a new video game was released that day?

If A, B, and C are all getting their work done in the time that they are working, I think equally of the three of them, as subordinate, peer, or supervisor.

Bingo.

A, B, and C should all just leave at a regular, reasonable time. And sometimes each of them has reason to leave early, and doesn't need to justify it.

Employee B: [to prevent burnout so that I can remain a functioning member of society.]

As you posted down below, this should all be seen equally if the person is getting their work done, but it's not, and that's the point I was making.