Regarding your last point, it basically ignores everything about the "mythical man month" concept. Work and productivity are usually not evenly divisible into discrete chunks. When we had an economy dominated by factory work, where workers attached Widget A to Bracket B, you could divide things fairly evenly between workers.
But today most jobs that aren't just physical labor benefit from having employees around more often. They stay up to date more easily, they can communicate what they learn more quickly, they can code for hours straight without the interruption of leaving at 2pm (not to mention all the interruptions due to meetings that would have to be compressed into shorter workdays to keep them up to date).
There are also economic benefits of longer work days. A smaller fraction of a person's time is spent commuting (in aggreggate, cleaning up the roads and reducing carbon emissions due to fewer workers per company). And in the US, where we have decided to couple a person's insurance and benefits with his or her employer, the non-salary costs associated with an employee are a very significant component of the total cost of that employee, companies have a big disincentive to hire a large number of people, even when the work can be evenly divided into small chunks.
> Regarding your last point, it basically ignores everything about the "mythical man month" concept.
This is true. I would propose that we are, or will become, wealthy enough to absorb any inefficiency.
> There are also economic benefits of longer work days.
I agree with this as well. In fact, I think we'd be much better off with norms of 3x8, 3x10, 4x8, etc. A work week of 5 half-days would be deeply sub-optimal. (Maybe these are just my own biases.) :)
But today most jobs that aren't just physical labor benefit from having employees around more often. They stay up to date more easily, they can communicate what they learn more quickly, they can code for hours straight without the interruption of leaving at 2pm (not to mention all the interruptions due to meetings that would have to be compressed into shorter workdays to keep them up to date).
There are also economic benefits of longer work days. A smaller fraction of a person's time is spent commuting (in aggreggate, cleaning up the roads and reducing carbon emissions due to fewer workers per company). And in the US, where we have decided to couple a person's insurance and benefits with his or her employer, the non-salary costs associated with an employee are a very significant component of the total cost of that employee, companies have a big disincentive to hire a large number of people, even when the work can be evenly divided into small chunks.