So, this would seem to be fairly easy to test empirically. Get a reasonably object measurement of the quality of writing, and use it on something where you know if it's true:

1) court testimony which we know (from outside evidence) is either true or not true 2) scientific papers which we know to have been reproducible, or not 3) stock pundits predictions about the future of some company or other, which we know with hindsight to have been accurate or not

Much more convincing to me than any amount of good writing about writing, would be to have some empirical evidence.