OK I'll bite. What are these fields? I think it is fanciful to call 4 hours per day 'normal'.
As you suggest, efficient meetings aren't really possible when people are overworked. Even one-on-one conversations can fall apart when sleep deprived. I've had work-related conversations at the end of an overly long 8h day where neither one of us could form coherent sentences about the code we were discussing. In an ideal world, we would have left work two hours prior.
I'll agree with you in general on this one (though perhaps then you should be happy with s 'standard job' salary), but disagree with OP.
Not quite; it's more like "most people aren't effective for more than four single-task focused hours per day, myself included, so everybody should be able to 'work' fewer hours."
Working on a side project might use a different part of the brain or a different sort of willpower reserve, so it's entirely possible that someone will fall asleep after four hours of actual work, but could then go home and spend another two hours on something completely different.
Like the new head of our CS department said: he doesn't really care if his professors spend most of their time in the office or at a cafe -- as long as they're comming up with new ideas and do research (the institute has a very high rate of publication for its size).