I've been circling around this idea for a while but just didn't have the words to express it correctly. But now I think I've got it. It seems to me that:
Marxian political economy is usually quite good. Marx and those he inspired tend to have remarkable insights into the workings of capitalism. Furthermore, Marxian theorists tend to be able to see past the smoke and mirrors of the hustle, to see things as they really are (which sets them apart from liberal and neoliberal thinkers who become so intoxicated by the film flam show that they eventually become a part of the hustle).
BUT, Marxian ontology (theory about the nature of being) is often woefully inadequate. Marxian ontology seems to have a couple of different variations -- 1.) that capitalism is what corrupts and if we could just get rid of capitalism everything would be better or 2.) the bourgeoisie is inherently corrupt and if we could just replace the bourgeoisie with the proletariat everything would be better.
But it seems to me that 1.) capitalism is just one of many things that can corrupt; and 2.) that all human beings (regardless of what station in life they are born into) are vulnerable to corruption.
So what happens if we marry the Marxian critique of capitalism with an ontology that says that all human beings are prone to corruption, that power corrupts, and that we need checks and balances to rein in the natural human impulse towards corruption?