Thanks to helpful commenters on the original post, especially Kaj Sotala. It's mostly thanks to Kaj that, three months hence, I've now changed my view.

Three months ago, I wrote a post called AI Can’t Write Good Fiction. The subtitle was “Yet, at least”. Good thing for the subtitle, because now maybe it can.

Here's a (very short) story written by Claude 4 Opus, at my minimal direction:

Sam's alarm didn't go off.

She woke to sunlight and the sound of Kai making coffee in the kitchen. He'd left for his run already and come back. She could tell from the particular way he moved around the counter, post-endorphins quiet.