> Courts (at least in the US) have already ruled that use of ingested data for training is transformative

Yes, the training of the model itself is (or should be) a transformative act so you can train a model on whatever you have legal access to view.

However, that doesn't mean that the output of the model is automatically not infringing. If the model is prompted to create a copy of some copyrighted work, that is (or should be) still a violation.

Just like memorizing a book isn't infringment but reproducing a book from memory is.