As one of the most prolific writers to ever have tackled Superman, Grant Morrison. believes that the Man of Steel has a weakness even greater than kryptonite: writing. Morrison's pen is arguably best known for writing one of the most quintessential stories in the character's most recent history, All Star Superman. In addition, Morrison contributed to several Justice League stories as well as The Multiversity, where they created Calvin Ellis' Superman character. Most recently the writer crafted the limited series Superman and The Authority.
Superman and The Authority has been praised for bringing the title character back to his root values. Morrison obviously took a more classic approach to writing Clark Kent, which is a route Morrison often takes for the character, but they also could have nearly gone into a completely different direction. It was not too long ago that Morrison spoke in-depth about DC wanting them to write Superman as an evil authoritarian, similar to how he has been infamously portrayed in the Injustice franchise. Under the impression that Superman being a tyrant goes against everything that the character stands for and represents, Morrison refused.
In a recent Substack post, Grant Morrison goes more in-depth about DC's plans, but more so in the context of Superman's greatest weakness, and they're not talking about kryptonite. As they go on to explain, Morrison states that Superman's greatest weakness is that he can't resist the writer's will and must do whatever they command (these thoughts have been paraphrased rather than quoted, according to a request in Morrison's original blog post). The same can be said for every fictional character and speaks to what is perhaps a recurring, nagging flaw that sets back the character in any medium he's produced in.
A common criticism from both fans and critics is that Superman is just some boring boy scout. This has led to many recent portrayals both in comics and in movies trying to reorient the character as either edgier or simply evil. The idea of an evil, tyrannical Superman was at one time a fascinating re-contextualization of the character that has now become a tired cliché, used as a go-to when the idea wells are running dry. Ironically enough, evil Superman has earned as many criticisms as boring Superman has, rendering the whole tool counter-productive.
All of this speaks to what Morrison's assertion that writing can be Superman's biggest enemy sometimes. Story choices such as turning Superman into an evil tyrannical contradict what fans have come to know about Superman's character and go against the larger general symbol for what Superman stands for. Regardless, it can still happen as long as the writer wants to see it happen. No matter how nonsensical, Superman has no choice but to do what he's written to do. Grant Morrison understands better than anyone that Superman succumbing to the whims of a writer poses a stronger danger than kryptonite ever could.
Source: Grant Morrison