It's right that they steer toward the center of their distribution. But I would offer a different view on whether that's a step up for half the population.
Writing isn't a distribution on a single dimension that goes from "bad" to "good". It's a lot of dimensions that encompass everything from "funny" to "formal", "precise" or "hysterical". They may be filled with metaphors, or use allegory; they may use math or logic to explain. The allegories could be from science fiction or they could be Biblical or 19th century Victorian novels. None of these are right or wrong, but they are opinionated ways to express an idea.
Writing feels better when it has real texture and character to it. That character is not the monodistribution of "bad" to "good". It's whether it inhabits pockets of out-of-distribution thought in the thousands of dimensions of "thought-space."
An LLM pushing to the center of distribution means it pushes the writing out of inhabiting any of the interesting pockets that create the feeling of texture. The middle of the distribution does not mean it is average quality: it means it's not good at all. The median of the distribution can be far worse than the median writer if you accept that the median writer has out-of-distribution thoughts on at least something, and that it is this which makes their thoughts interesting.
That's why a rough, perhaps not-totally-grammatical article written by someone with interesting thoughts is vastly better than a "correct" LLM revision, even if the human writer isn't a 'good' writer. Their article occupies an opinionated stance on some dimension that matters; it sits in a pocket of interestingness that LLMs seem almost totally unable to inhabit.
The exact middle of the distribution across thousands of dimensions may actually be one of the very worst places of them all.