work (excluding production line blue collar jobs) expands to take up the hours worked for example back in the 70's the Uk went to a 3 day week during the power strikes funnily the output of the country did not go down by 3/5.
Perhaps the overhead could be considered as part of the overall costs. I would still appreciate the choice of having to work 75% of the time for 65% pay if I understood that the difference was due to health coverage and other benefits. In other words, the transparency would help. I strongly believe I'd still sign up for it.
This assumes a linear relationship between hours worked and amount accomplished. I doubt such a relationship holds after 5 or 6 hours. I bet many programmers would get more done in a 6-hour day than an 8-hour day, due to increased energy.
If we could drop it so everyone worked 30 hours but worked 75% of what they do today, many would jump at it in the higher earning echelons.
Per worker costs strongly incentivise long weeks.