Publishable doesn't mean marketable that being said. Everything may be quality but if an agent doesn't think they can sell it...This is probably true but not necessarily helpful. We can't see in the submission box, so we don't really know if we're in the 80 or 20%. Also, it's not so cut and dry. Someone might have a fantastic premise and storytelling that overrides the "quality" of the writing. They'd probably still be considered publishable.