I'm not the best person to ask about this issue. In general, I say a story needs to be long enough to satisfy its promise in a fulfilling way. What I do see is that if someone can create story magic, stories that transport an audience, people respond to that. A student wrote an enchanting screenplay that was completely uncommercial. A major Hollywood producer loved the story and asked her to work as a reader.
Good things happen to people who can create story magic.
I teach people to create a strong story foundation. I've found that until struggling writers can accurately break down, scene by scene, a movie, play, or book and understand the mechanics of how a particular story is being told, they struggle to write dramatic scenes. Such writers don't recognize the difference between what they are doing and what successful storytellers are doing. I'm not suggesting what I teach is any kind of magic formula. I've found it generally takes people two years to fully internalize what I teach and begin to write in a way that evokes a story journey, not simply describes the journey.