In practice, this is a tautology. People pay for inefficiencies, but inefficiencies are defined as what lose money. You didn't say anything, you just diluted a (wrong) theory to make it correct and as a result don't have a theory anymore, just a rhetorical trick.
Do you have an example of an economist making that argument, outside of theoretical modeling?
I don't see the tautology. One person in a leadership position may value certain things and be willing to lose money on them. The cost gives their peers and supervisors at least one reason to question that practice.
As far as economists making that argument, take a look at the strong and semi-strong EMH. Plenty of economists agree with the semi-strong version.
Note that these theories are actually generally descriptive, no one wholesale invented capitalism. For the entirety of human history we have had systems based on a combination of markets, status, family lineage, etc. this applies both to the past and to today.
What I’m taking issue with is the degree to which all of that is glossed over and people assume that the market will evolve naturally if left unspoiled/untouched.