> AI writing is almost indistinguishable from human writing

This depends on what you consider AI writing. If I dictate what the AI must write word by word verbatim, is it considered AI writing? Is it something to do about the percentage of the text generated? Does it have to do with the vocabulary the AI knows? What if I don't know any other words than the AI does? Does it have to do with the efficiency of communication?

Nevertheless, I don't think AI writing can ever be human writing. No matter if it uses the same words as a human and it's indistinguishable. This is because humans participate in a society as independent conscious actors and thus communication has meaning. The only way text can become communication is when the writer has intents, they're willing to participate in society.