I think if you take someone like me, and really most people, and have them sit in the office for an extra hour per day, you probably won't see much benefit. But I definitely feel like there are some people who grind work all day, putting in ridiculous hours, and they do amazingly work, beyond what 1.5 or even 2 people can do. Especially when you consider career progression over time, maybe the people who are hustling will have ranked up a couple times over an 8 hour/day person, and is contributing at a much higher level.

I think you make a good point that it's more complicated than "just stay longer", but I do also agree with GP that there is some kind of compounding interest when it comes to how many hours work. Don't know how it works though.