The law has always been able to recognize a distinction between Hunter S. Thompson reading Ernest Hemingway and learning from his style and a billion GPUs reading a billion books to be able to produce it on demand. It takes time for the law to catch up to the technology but it will.
It's not a hard problem to solve, you scale the punishment for the cases you prosecute so high that it makes the expected value of stealing a suitcase negative
ChatGPT is already capable of producing writing far superior to the average or even above-average native English speaker, as long as it has a reasonable statement to make provided in the prompt. So, we're already at the point where (most) humans can't do better.