I think the quality of wfh really depends on the person and if they have enough integrity with their obligations to begin with. Sure it would be simple to get away with barely doing anything, but the people who do this are probably not who you would want to hire anyway.
Open plan offices tend to be productivity-destroying for technical work that requires concentration. I assume they were largely adopted to save money, as a status indicator vs. managers with private offices, for surveillance, and for appearance.
The only open plan approach that I have seen work is a library where noise is forbidden and private work carrels are provided.
Unless they work from overseas for $15,000 salary.
At home I can structure the day around my own concentration and have uninterrupted flow for hours and actually get shit done.
Sometimes my feeling is that managers hate home office because that means they have to stop walking around and chatting with people.
Also "Work less" doesn't convey the negative connotations you seem to think it does if they're meeting their contractual expectations.
Unfortunately some managers seem willing to accept a productivity loss if it allows them to feel more important.