Writing is editing. AI is not good at line editing or structural editing. It beats humans on quantity, but it hasn't been taught the basics: show not tell, avoid adverbs, avoid long sentences, try not to repeat yourself, keep the story consistent.

AI has been trained to not be biased. This is good of course, but when you write a story, you have to choose a side. You need to choose a coherent setting and cast of characters. So in the absence of personal preferences and history, AI can only choose the most prevalent patterns in the training data or random stuff. This means clichés or something incoherent. Also the training data is not up to date with modern ideas AFAIK. It leans toward books written before 1920.

So I think the question should be when can AI edit properly? When and how can it build a personal style and history? I don't think that throwing money and data at this is enough. Knowledge of psychology, neuromorphic hardware, spiking neural networks, extreme learning machines, or something else entirely is required. So a decade is probably insufficient.