Your conclusions don’t follow. Most people are not doing exclusively mentally demanding technical work, which you admit, so why would you limit the work week based on that? And non strenuous work takes a nontrivial amount of time? I’m regularly solidly productive for 30-40 hours a week (tracked with RescueTime app).
Today I did around a dozen PRs (among other things like design reviews) that were tiny changes (cleanup, or migration config flags over various repos). It wasn’t hard work, but it’s important work that has to get done. Shortening the week doesn’t magically get this done faster.
A lot of time spent doing "hard" things is unproductive. So many times I've worked on a hard bug long fruitless hours just to come back the next day and spotting the problem almost immediately. Quick cleanup tasks are important yes, but most of the time you can delegate those to newer employees that can actually learn from them.
Just because the journey feels unproductive doesn’t mean you can cut the journey in half and get to the destination. Who says your brain would have still found the bug without the time invested in it that you’re interpreting as “unproductive”? Who says if you r brain didn’t need that investment in the big just a break that a break working on other productive things wouldn’t have been just as good as a day at the beach?
Also I do give my newer employees smaller easier tasks, but they still need review, mentoring, etc. which is just another “not hard activity that takes time”. One again the idea that you can just cut work hours with no impact seems silly unless you’re working like 70 hours, or unless you’re already just a voluntarily unproductive worker. Maybe that’s an underdiscusssd angle to this; some people just don’t know how to productively organize their time.
Today I did around a dozen PRs (among other things like design reviews) that were tiny changes (cleanup, or migration config flags over various repos). It wasn’t hard work, but it’s important work that has to get done. Shortening the week doesn’t magically get this done faster.