I felt that this was obvious. Why should this be made explicit? Asking sincerely; it seems obvious that the subjects live in practically different countries.

Because the observation that they're all relatively happy is contingent on where they're anchoring their self-worth. If the barback gets to hang out for a day with the CEO he's going to realize that he's working hella harder for a fuckton less money and it's not going to make him pleased. Meanwhile the CEO is going to realize that poor people make him uncomfortable because goddamn it, Jerry down the street bought a Viper so it's not like he's a bad person and he doesn't think he should feel guilty for wanting a Tesla because it's zero emissions, for god's sake!

Wealth and happiness studies need to be done independent of social stratification or else the results get all fucked up. That's why that cutesy "we're paying everyone $72k" company was such bullshit - the guy who has been doing his job for twenty years feels entirely entitled to make more money than the guy who's been there for six months because fuckin' A, the company's ability to pay that much has been made entirely on his back. Which gets even worse when you have people whose wealth is clearly not derived from their effort or expertise.

What's the public policy lesson? Eager to hear it.

That when you hide the actual impact of taxes from the people who are paying it, everyone will assume that it's all being wasted. That's the biggest problem any form of socialism faces in the United States - we know we're paying for bombers, we know we're paying for space shuttles, but we have no idea how much is going into education because we still have to pay for that shit with bake sales.