I've been in that exact position - we kept hiring high powered sales guys and expected them to sell a product that was close, but not close enough, to what customers actually wanted.
It's the classic mistake of confusing sales (selling an existing product) and marketing (finding out what people really want).
That's a great point. There is a third branch in the trifecta, which is advertising/PR to tell people about what you have.
Be wary of someone great at advertising/PR but not at market fit. Those are two distinct questions. Often the founder needs to "own" market fit, probably with the help of others, and advertising/PR can be somewhat delegated. However since market fit drives every decision, it can be hard for that person to be anyone else but the founder.
It's the classic mistake of confusing sales (selling an existing product) and marketing (finding out what people really want).