The crux of your argument doesn't hold water outside of economics circles. The power imbalance between parties makes "simply declining" as real a possibility a

The crux of your argument doesn't hold water outside of economics circles. The power imbalance between parties makes "simply declining" as real a possibility as Plato's Forms. In a perfect world with almost all degrees of freedom removed, yes, you're correct. But the world is not perfect, ensuring a beneficial transaction to both parties for every transaction is simply intractable without infinite time/computational resources to brute force a solution, every time. To expand on the dogmatic proclamations economists are prone to making, this is why almost all natural and formal scientists have conscious or unconscious disdain for the claim that economics has a claim to the same epistemological rigour as other sciences. You can't extrapolate results and lemmas from within a domain of discourse to the outside world. Even the best economic models and the real world are not isometric. Implying that they are has so far resulted in some fantastic and incomprehensibly efficient systems but also an untold amount of human suffering.