I understand this thinking. I think, though, that the more we understand about cognition (and sleep and health in general and its impact on thinking), the more we'll tend toward somewhat lighter hours (more like 30-40 hours a week even in a startup situation). Not because we can get away with it, but because the output is actually superior.
From a business strategy standpoint, my experience has been that sometimes companies try to compensate for poor strategy by piling on the hours. To me, it's like trying to do push ups to solve math problems faster.
Similarly, I have noticed that strategic structural soundness is vastly more important than hours worked. When the structure is there, all your efforts are leveraged many times over such that, effectively, 30 hours a week becomes more like 300.
Hard work is important and satisfying but duration is not the real measure we should look at, imo.
