It sounds to me like your teacher's "Five Act Formula" is more suited to Hollywood blockbusters than literature.
My understanding is that LotR is replete with examples of how, in literary theory, one is supposed
not to write a book. I am sure that I will be corrected if I am wrong (Bęthberry?
), but I believe that the separation of TTT and RotK into two distinct halves (Frodo and Sam/Aragron and co) would originally have had literary theorists tearing their hair out. His use of "archaic" language too has, I believe, been criticised as inappropriate in a "modern" novel. I am sure that there are other examples.
Of course there are tried and tested formulae, but it is in challenging and redefining traditional structures that the most groundbreaking works can arise. Tolkien started out writing for his own pleasure, to provide a setting for the languages that he had invented, and therefore had no mind to resort to literary formulae. The fact that LotR has become one of the most popular novels of modern times rather gives the lie to the argument that there is only one way to write a book.
I would add that the need for "blockbuster" films to fit the preconceptions of studios and investors as to what audiences want lies behind many of the changes made in the adaption of LotR to the silver screen. Jackson does rather "buck the trend" in one or two places (such as in insisting on the inclusion of Frodo's departure to the West and, indeed, in carrying out much of the filming for all three films in one sitting), but on the whole, he had to stay within established boundaries in order to get the financial backing that he needed.