You can, though.
Not as easily, but it has been quantified.
https://scholar.harvard.edu/files/nataliaemanuel/files/emanuel_jmp.pdf
https://www.waldenu.edu/programs/business/resource/shortened-work-weeks-what-studies-show
We know these things for pretty much certain. The only people who pretend “the science isn’t in” are the people who stand to gain when employees are exploited. So, ya know…