I think we're agreeing more than we disagree, but I'd point out some sections from the 2005 IGDA post on work in the games industry a.k.a. "reaction to ea_spouse" at
https://igda.org/resources-archive/why-crunch-mode-doesnt-wo...:
> Ernst Abbe, the head of one of the greatest German factories, wrote many years ago that the shortening from nine to eight hours, that is, a cutting-down of more than 10 per cent, did not involve a reduction of the day’s product, but an increase, and that this increase did not result from any supplementary efforts by which the intensity of the work would be reinforced in an unhygienic way. This conviction of Abbe still seems to hold true after millions of experiments over the whole globe.
This was written 1913, about the time when Ford's automation was just getting going - the "many years ago" and the fact that Abbe died 1905, shows his studies were referring to a time before Ford's production lines and efficiency gains.
> That output does not rise or fall in direct proportion to the number of hours worked is a lesson that seemingly has to be relearned each generation. In 1848, the English parliament passed the ten-hours law and total output per-worker, per-day increased. In the 1890s employers experimented widely with the eight hour day and repeatedly found that total output per-worker increased. In the first decades of the 20th century, Frederick W. Taylor, the originator of “scientific management” prescribed reduced work times and attained remarkable increases in per-worker output.
This too is from a pre-Ford time.
So I would reply that while Ford's innovations might have compounded any gains from shorter working hours, such gains have been found in many other places and times. indeed, the IGDA summarises their evidence by saying "five-day weeks of eight-hour days maximize long-term output in every industry that has been studied over the past century".