It’s one thing to walk onto the set of an existing franchise as the new person, but in the case of Avatar it’s a bit more than that. James Cameron created a new world when he created Avatar and he went much deeper in creating this world than many writers do. The Na’vi have their own language which functions like the real thing. The planet Pandora is full of life, even if the majority of the animals there are hexuped while the Na’vi are quadrupeds, which makes no sense. James Cameron put a lot of work into building this world and so step into probably feels quite different than just walking into any franchise. Especially when you’re the only one who doesn’t speak the language.