> And most of the world is not zero-sum...

That is a strange thing to say, especially now.

Clearly, there is a reason Von Neumann spent so much time on this 'zero-sum' formulation of the problem, specifically in economics. Clearly he must have believed this was representative to a significant extent, especially given his interest in pragmatic problems.

It would make no sense for an intelligent person to work on an economics problem which doesn't model reality.