Cosmology and Metaphysics in Fiction: Liberatory or Constraining?

The inspiration for this post came from an interview that I read recently with Kentaro Miura, the creator of the manga series Berserk. Miura is commenting on a particular chapter of the manga that he explicitly omitted from the tankoban collections. The chapter in question involves one of the characters encountering and conversing with the "Idea of Evil", or the Berserk universe's analog of God. When asked why he omitted that chapter, Miura said that by introducing 'God' he had 'given away' too much information about how the universe that Berserk takes place in operates. Miura said he wanted to give just enough information about how the Berserk universe is situated, as he felt that too much detail would constrain possible future developments of the story. Now, in a lot of fiction and fantasy, authors put a ton of effort into creating the cosmologies and underlying metaphysics of their fictional universes. Tolkein has an entire mythos about the creation of the world and a metaphysics about the structure of reality for his Lord of the Rings series, and many sci-fi authors ( I am thinking of Orson Scott Card and his universe of 'philotes' as an example) create a cosmological background in which their stories take place. I find myself wondering if Miura's worry is a legitimate one: does the construction of these fantastically elaborate cosmological systems in fiction ultimately constrain the possible development of said fiction? At first glance I may think so. Authors who have created these elaborate systems may feel pressure to conform every detail of their story to fit that system, and ultimately limit the kinds of events, processes, or entities that the author would feel comfortable putting into the story. Sometimes, an otherwise unspecified explanation of an event may suit the story just fine. On the other hand, having theses complex mythologies in place does give an element of consistency and realism to the fictional universe that would otherwise be absent.