(Most) humans aren't supposed to work 80+ a week. I say most because there are always those superhumans you come across that just seem to be able to do it; but most can't.
I always try to look at statements like this through the eyes of a would-be programmer. If I was about to start down the programming route and was told I could never achieve my aims without accepting an 80 hour work week then I'd run a mile.
I don't think they're superhuman, they are people who have no lives and will burn out in a short period of time. I can only feel sorry for them.
An example of this is academia where every prof I've met 'works' insane hours but are completely (and happily) absorbed in their fields. The whole thing feels like a hobby to them. The only thing they'd want to get rid of is the paperwork (research assessments, etc) so they could spend that time with students and research.
If you do stuff you don't really like or it's 'just' a job then I wouldn't even work 40 hours for it, but I really don't see what's wrong with 'always on' if this happens to be your life.
But the other argument is that, after so many hours, returns on effort are reduced, and I don't see a good argument for this being not true whether a person is in love with their vocation.
I would posit that a likely scenario, is that the 80-hour-a-weeker's passion for their work their concern for efficiency. They don't get as much done per hour, but they don't care as much because they love the parts even where they are just plodding along.
"Losing sleep to hit a deadline the next day is valid, but it isn't a productivity enhancer. I have always needed a full 8hrs for good work." https://twitter.com/ID_AA_Carmack/status/436351780243259393
So its got more to do with extended concentration on one task, vs the actual hours? If the work has several tasks (e.g. rehearsing, the gig, songwriting, negotiating) then maybe its not the same as sitting in front of a screen the same time.
The multitude of tasks bit is true. Where my BS meter starts to twitch is when it's a developer telling me that they've been hacking 12 hours a day for x years and feel fit as a fiddle. In those instances, I've gotta imagine the quality output vs. time quotient is lower per capita than the average 30-50 hour per week dev.
Compare it to other things, say for example, musicians.
When a band goes on tour, it could be looked at like they're putting in 168 hours a week. Really though, they're doing maybe 8 hours a week of actually playing in front of people, maybe like 5-15 hours of practice, and that's all the solid "work" they're doing. That's not where the job ends though...100% of their life is their job because they are always potentially writing new material.
If I'm coding for someone else in exchange for money, that's work. If I do it on my own time for free, it's not work. That's a pretty clear distinction, since I can't do both at once.
Whether they suffer some epic burnout in years to come remains to be seen but I hope not for their sake.