This article could go in lots of different directions. Consider writing a series on it.
I have one of those jobs where I do one hour of “real work” for each three hours I am employed. But the nature of my real work is that I’m not sure when those real tasks are going to happen. I have to work my full shift to be available for when the real work occurs.
BTW, I do have a side project to work on when my work tasks are low. Maybe my employer will benefit from this side project some day. But I recognize that many employees do not think this way: they would use idle time to be idle.
The turning of full-time jobs to part-time jobs to not pay benefits to employees is not a good sign that society is progressing. But if we had a UBI, this would be less of an issue.
As for Americans (and many westerners) working more hours, I would say that many are making a free market choice. There are lots of people who are beyond a subsistence level of income, but still yet freely choose to work overtime to get themselves into a more materialistic lifestyle. I think your study needs to segregate those people who must work overtime and those who just want to buy more things.