It's hard to judge. There's the little matter that the metacognitive skill to judge whether a piece of prose is a best-seller or should be taken out back and mercifully shot -- correlates with the skill to write it in the first place. It's been reproduced in the lab: Unskilled and Unaware of It.
It explains a great deal. Like slushpiles. (If you're not familiar with them, check out Slushkiller.) It explains why the early stories are embarrassing only with hindsight. It explains why you may get less happy with your work the more you do of it. . . .