If you complete X amount of work in 5 days, then switch to 4 days and still complete X amount of work, then it seems like you can actually complete X + X/5 in 5 days instead of X.
I'm not arguing how much you should or shouldn't work. I'm just pushing back against the non-sense that people actually accomplish more by working less.
Thought experiment: someone is forced to work 23 hours a day with 1 hour for sleep, 7 days a week. They will likely be fairly productive the first day, but eventually their productivity per day will be zero as they are too tired to function. Over, say, a month, their productivity will be, lets say, 40 hours (wild guess, maybe 20 hours one day, then a scattering the rest of the month).
Now how about who someone works 4 hours a day, 5 days a week. They are likely productive those 4 hours, and able to sustain that the entire month. So they get 80 hours of productive work done, even though they 'worked less'.
Now those are extremes, but literally working less in this case results in higher productivity in the long run. Now where that point is depends on very many variables (including individual biology, social responsibilities, and type of work). But such a point does exist where working more hours results in less productivity.
I'm not arguing how much you should or shouldn't work. I'm just pushing back against the non-sense that people actually accomplish more by working less.