Yes and no. In no way was it created as a holistic whole. Indeed, a great deal of it was published posthumously, edited by his son. Tolkien was not like JMS, with the whole arc worked out in most detail before he began.
Who or what is "JMS?"
And of course it wasn't created as a holistic whole. It was created bit by bit. But the world and story 'existed' before the LotR was written, and thus LotR grew out of an already existing, organic, and holistic world. And yes, he continued to work on it for another 30 years after he finished LotR, deepening it, fleshing out details that never made it into LotR. Actually, he wrote an excellent story, Leaf By Niggle, about his never-ending creative process, how perfection is never achieved.
But one of the things I'm trying to get at is that, from Tolkien's perspective, and I think from the perspective of most diehard Tolkien fans (or Tolkienistas, as I think Michael Moorcock called them, or was it China Mieville?), LotR was secondary to his larger artistic process. His magnum opus wasn't LotR or the Hobbit or even the Silmarillion. It was Middle-earth, and those were just expressions of it on paper. Whereas, to use your example, Fast and Furious is its own thing. Certainly there is a body of "lore" that has been accumulated from all the movies, and I'm guessing someone has made a F&F wiki (I've never even seen a single F&F movie, so have no idea). But all of the F&F universe was created to serve the story, the films being all that really matters; they
are the prima materia. Tolkien's books--not to mention the films--were expressions of his artistic project, not the thing itself. And I think that's partially why Fall of Gondolin matters, at least if one wants to really experience the heart of Tolkien's creation, his own prima materia: Middle-earth itself.