The problem is that the above line of reasoning provides no reason to believe that the "marketing world" at the peak of function B is any worse than a random world at any lower threshold.

True. Which is why I added arguments pointing that a marketing world will likely be bad. Even on your terms, a peak of B will probably involve a diversion of effort/energy that could have contributed to A, away from A. eg if A is apples and B is bananas, the world with the most bananas is likely to contain no apples at all.