I think “strong case” is probably reliant on a few points on the output side, and would have to be more than just author/artists style.

Style itself would be very hard to deem infringement, for obvious reasons (idea) - I think it’s much more likely an issue when a character has derivative elements (e.g., iron man, spider man esque features), and where the users prompt had explicit references to those characters (intent)

All that said, even then, on the artistic side I think it would come down to the same analysis that would apply to traditional media - AI is just a vehicle that introduces some novel risks.

Music might be more risky given the litigious nature of the industry.

Code? It’s going to be hard to claim infringement with dramatically different implementations, barring patent coverage.