Cowen, like most defenders of capitalism, seems to confuse capitalism with free markets & socialism with planned economy. (Non-economists who aren’t writing books can be forgiven for being confused in this way, since the most visible and vocal socialist project, the USSR, had a planned economy.) This means that their criticisms often fail to land, because they’re not criticizing what actual marxists mean: it’s possible to have a completely communist system that has free markets, for instance, and our current capitalist system is dominated by large vertically-integrated planned economies (albeit ones that don’t correspond to states very well).
So long as we translate the terminology carefully, we can synthesize marxist economics with non-marxist economics & gain useful insight: the primary problem with non-marxist economics being that, pragmatically, they systematically underestimate how insulated decision-makers are from market forces & systematically overestimate how much freedom-of-informed-choice (and thus, control) customers have. (On this point, Thiel is right: the goal of any capitalist is to insulate themselves from the need to add value and become a rent-seeker, whether by monopoly or by financialization. Thiel thinks this is a good thing, and it’s a good thing for people like Thiel who can play that game, but it’s a bad thing for everybody else.)
It is in this way that the left writ large should learn from capitalism (and this is in line with history: Marx’s greatest achievement was not inventing communism but inventing capitalism by writing the first systematic analysis of it; meanwhile, communism he left quite vague).