Responses of this form -- if X were worthwhile, X would already be happening; as X is not happening, it cannot be worthwhile -- are often proposed when talking about the economy. Is this not presuming the answer?

It reminds me of Leibniz's idea that we live in the best of all possible worlds [1], except the omniscience & efficiency of the market stand in for God.

If the way in which we hope the economy picks good outcomes involves people thinking of things that might be worth doing, trying them and then succeeding if they were right, we surely must allow that not all of the good ideas have already been had, and so we do not yet live in the best (most economic?) of all possible worlds?

[1] https://en.wikipedia.org/wiki/Best_of_all_possible_worlds