Good point. Worldbuilding is necessary and I would risk saying it is something you got to have done before you even have your story ready. At the very least, where the story takes place.
I will give an ounce of credit on the team: I believe Vivianne did write about Hell and Heaven. She needed to flesh it, and how it would affect our world. Furthermore, does it work as a "Alice In Wonderland"/Narnia setpiece? Meaning, parallel world to ours, where there's interactibility? Of course. But what about humans who want to access Hell and do things in it? Take a concept from Doom, where Argent D' Nur, where you have a hellish landscape. Using "demonic" energy to solve an energy crisis on Earth. There is potential.
Even if it seems "boring", the writing has to be developed. I'm sure on GRRM's case, he didn't have Essos done by the time A Game of Thrones was published - just Westeros and the Free Cities of the Narrow Sea. "Essos" got its name only after
A Feast of Crows was released, by 2008. So there is some leeway here and there. Yet you must absolutely need to have cultures, ideas and certain things laid down, even if you want to do "L.A. but gayer and written by a fujoshi".