I worked at lots of places with official 8 hour days. In reality some (senior) people worked 6, and many (junior) worked 12-16. Hard to imagine a top down law limiting working hours will have much effect. It's attacking the cosmetics of a symptom, and not the real cause.
That said... Let's list several big ifs...
If... The last few marginal hours are more productive than hiring someone new.
And If... The economy is a zero-sum game. (For my company to make money, yours has to lose it)
And If... We can coordinate everyone in the world.
And If... We can enforce it.
Then doing something like putting a formal limit on hours makes sense. This is much more in line with a communist/socialist world-view.
Enforcement of the Working Time Directive varies a lot within Europe, but in many countries it is quite strictly enforced for most roles (at least for companies of more than a certain size).
I previously worked for a private French firm with ~700 Paris based employees. They worked very long hours, even by US standards. I thought, "If it can't be mandated here, it can't be mandated anywhere."
Hmm, that's quite surprising; in Ireland, at least for large companies, it is generally enforced fairly well (though there's an ongoing problem with the hospitals; it turns out there aren't really enough doctors if you can't make them do overtime), and France is generally stricter about this stuff than us. Were these normal employees or some sort of weird contractor arrangement?
Normal employees. We had an Irish subsidiary too, though I never visited and saw the hours they put in. My impression is they were very industrious. (Though industrious doesn't have to connect with hours)
Ireland is usually industrious without long hours. There was a UK based study on it recently that gave positive results. I can't find the link at the moment.
That said... Let's list several big ifs...
If... The last few marginal hours are more productive than hiring someone new.
And If... The economy is a zero-sum game. (For my company to make money, yours has to lose it)
And If... We can coordinate everyone in the world.
And If... We can enforce it.
Then doing something like putting a formal limit on hours makes sense. This is much more in line with a communist/socialist world-view.