Average ChatGPT output for the most part reminds me of the average British politician who can waffle on until you stop them, talking about all the aspects of something, but never really answering your question with all that much substance and depth, sometimes not even answering it whatsoever. Very "30,000 foot view".
Good writing only comes from writing lots of things that other people actually want to read. Course work is poorly structured for that, it isn’t peer review.
And whilst it's bad at being nuanced, it's even worse at being opinionated because its guide rails and human testers alike love its answers to be qualified with generic caveats like "depends on the specific situation"...
If you ask me, this is very "con-artisty".
A ChatGPT answer looks exactly like a politician that doesn't want to tell you the answer to your question.
It also has a "high schooler" style, but mostly because of the rigid form it uses. If actual high schoolers throw random content in their essays like ChatGPT does, they will get negative points for that.
Having a diary is one thing - having creative writing that is in the open and subject to criticism and encouraging refinement is quite another.