Reasoning about humans as cogs is inevitably going to be a really awful way to get people and companies to be productive - most of it isn't that. However, humans, like plants, are able to survive and sometimes thrive in really terrible conditions _despite_ those conditions. This is what you see at Amazon; if you throw enough money at anything then you're going to get some kind of result. But, despite Amazon, Microsoft, and Google having billions and billions of dollars to throw at this stuff we mostly still grab for Open Source tools (and so do they). That's largely because the workflows the Open Source community use actually work and that's mostly because they get the human stuff right.
The whole "man hours - overhead = man joules" thing doesn't math and using that as a basis for any kind of analysis is going to lead to weird places. There are elements of human workflows that fit into these boxes - the really mundane work. Reasoning about mundane processes through this lens is maybe a good idea to the extent that mundane work can't be swapped out for more interesting work. The problem is that what we really want is to excel at the stuff that isn't mundane (the force multiplier shit) and that needs an entirely different framework that reasons about humans as humans rather than machines.