The problem with the premise is that an LLM is not on some continuum from a rock to C3PO. Your hypothetical sapient robot is not a more advanced version of an LLM, it is a categorically and qualitatively different thing. An LLM training is not the same kind of event as a sapient being learning.
If yes, you have to agree that personhood isn't sufficient for the right to free expression. If no, then the use of copyrighted art to train an AI can't be wrong in principle. You can only object that the model is not sufficiently conscious or not sufficiently a person.