Chris Claremont is a comic book writer. that is not the same as a screen writer, director or producer. A perfect example is JK Rowling. She is the writer of the harry potter books, which she was good at, however when she shifted to actually screen writing the fantastic beasts harry potter spin off movies and a film series she is in charged off, that has not gone so well.
A lot of the times what book/comic authors are best at is been primary consultants when people want to adapt their work to films. them taking full control of the movie and everything about the film is not really the best idea.