He was famous for ripping off other artists' work, yeah. I think thats why he's not considered in such flattering light. I know many well-trained artists who agree that he was a hack and plagiarist - but that was his thing, after all...
It's all about building up on other people's previous work.
https://www.nytimes.com/2021/04/05/arts/design/warhol-copyri...
https://www.natlawreview.com/article/supreme-court-takes-and...