> PMC is pretty much exclusively bourgeoisie and petit bourgeoisie
As usually defined (where by the 2010s it accounted for more than a third of American jobs), it's not. It's mostly proletarians, a bit of it is in the petit bourgeois, and a numerically irrelevant or even smaller numerically irrelevant slice is in the haut bourgeoisie (it's not clear to me if the upper end of the usual understanding includes the haut bourgeois who incidentally have the kind of job usually ascribed to the “class” but for whom it is not particular job reflects rather than is in any way necessary to the power they exercise over capital, but it makes little difference either way.)
The whole purpose of the designation, within Leftist discourse, is to identify and growing (even at the time first identified) segment of the wage-labor force as class enemies of the proletariat by inventing a new class label to apply to them, so as to justify why they aren't targets for solidarity efforts.
> PMCs (e.g. C level execs) of major corporations a often make out better than shareholders.
C-level execs of major corps aren't typical members of the PMC “class” by a long shot.