LLMs are very good at creating things in the style of existing work, but they aren't that great at re-creating existing work verbatim. For example, here's what happens if you prompt Midjourney to draw "the mona lisa": https://i.imgur.com/njOlL5h.jpg

Obviously these are attempts at recreating the Mona Lisa, but none of them are the Mona Lisa. Whether they fall within fair use is an entirely separate question.

It originally being pirated or not would not come into play if its a copyright violation or not. Its a violation if it's 1:1 and billed as such, otherwise its a parody or inspired by