Books.

Why does this have to be pointed out every time? Sure, the story is meant to be taken as one big novel, but there's pretty clear differences in pacing across the three volumes.

The fact of the matter is that most people will be reading these books the way they consumed the movies: in three separate parts. Arbitrarily pointing out "well ackshully it's just one novel so please don't make that mistake again ok!?" when it doesn't even contribute to the discussion at hand just seems very pretentious.

Also yes OP Fellowship of the Ring does have some abysmal pacing between the Shire and Rivendell, but it gets much better from then on.

Yes and no. Yes Tolkien wrote it all as one work yet FOTR does have a narrative structure that isn't found in the other two volumes. I don't think this was done on purpose but it's interesting to me.