As it mirrors us rather accurately at least in terms of finding our mean/average behaviour/output. Our blockbusters are usually pathetically written, looking for the lowest common denominator to reach a bigger ticket buying audience.
The question for me isn't whether it can write Superhero movies but whether it could do a Billy Wilder/Charles Brackett or Orson Welles/Mankiewicz script. Or say Rob Towne's Chinatown or Coppola's The Conversation or Rose/Lumet's 12 Angry Men. Or Mamet's Glengary Glen Ross first as a play then as a film script. Or for that matter anything that Martin Mcdonagh writes. There's no real complexity of character, situation, atmosphere et al in the crash boom bang of clearly distinguished Heroes & Villains firing rockets & doing fist pumps.
The day they write those better than humans there'll be no strikes because there won't be many humans required in the movie making business anymore. Sadly such movies also don't find much of an audience anymore so maybe ChatGPT will take over the business anyway (even if it never can write like that).