“A person is fundamentally different from an LLM” does not need a legal argument and is implied by the fact that LLMs do not have human rights, or even anything comparable to animal rights.

A legal argument would be needed to argue the other way. This argument would imply granting LLMs some degree of human rights, which the very industry profiting from these copyright violations will never let happen for obvious reasons.

The other problem with the legal argument that it's "just like a person learning" is that corporations whose human employees have learned what copyrighted characters look like and then start incorporating them into their art are considered guilty of copyright violation, and don't get to deploy the "it's not an intentional copyright violation from someone who should have known better, it's just a tool outputting what the user requested" defence...