> I think it would be totally incoherent to say that copyrighted information is essentially fair game to include in your model but the outputs of your model are privileged against being included in other models.

IANAL, but going from copyrighted texts to an AI model likely constitutes a new original creation, not a slavish reproduction. Whereas going from one AI model to another is more likely to be considered a slavish reproduction reproduction, although arguably AI models are not copyrightable to the extent that the weights are objective facts, like entries in a phone book.