Rather when someone tweaks the content to avoid detection. Even today there are plenty of copyright material on youtube. They for example cut it in different ways to avoid detection.
Valid defense, no, but effective defense - yes. The reason why is the important bit.
The reason your average human guitar teacher in their home can pull up a song on their phone and teach you reproduce it is because it's completely infeasible to police that activity, whether you're trying to identify it or to sue for it. The rights houlders have an army of lawyers and ears in a terrifying number of places, but winning $100 from ten million amateur guitar players isn't worth the effort.
But if it can be proven that Claude systematically violates copyright, well, Amazon has deep pockets. And AI only works because it's trained on millions of existing works, the copyright for which is murky. If they get a cease and desist that threatens their business model, they'll make changes from the top.
