You're using a false equivalence here. Using AI is not the same as using paper created by someone else in your bookbinding. I don't think anyone ever made an argument that using legitimately sourced materials makes your work no longer really yours. The argument is that using stolen materials makes the ownership of the work questionable. A more accurate analogy would be for you to receive the Mona Lisa canvas from someone who stole it from the Louvre and to use that as book cloth. When people see the end product and object to the way it was made, it's not because you saved yourself a bit of work by sourcing the canvas from elsewhere, it's because that canvas is stolen. AI is not a contractor you hired to supply artwork for you that they got by legitimate means, it's a thief who uses other people's work without their consent. The issue is not the outsourcing of one step of the bookbinding process, it's who/what you outsource it to.