Haha I knew you were talking about Econ when I read the post. It seemed pretty clear it was PhD or gtfo when I did Econ undergrad. Masters seems like an actual scam.
Economics is one of the undergrad degrees that is often sort of generic--i.e. you don't really work in the field with just a BA/BS. And you need a PhD to actually be an economist so a Masters probably doesn't buy you much. (Not 100% true of course, but close enough.)
Yes, but many of the partners at those firms who are "economists" probably have PhDs.
I imagine it's also fairly common for banks, trading firms, and the like to have economists on staff but my point is that they're likely not mostly undergrad (or even Masters) economics majors.