In a forward to the edition I read of Watership Down there was an interview with the author, Richard Adams. He mentioned that he was often asked if the book is an allegory, and that it’s not.
It’s hard to imagine that a book that has quotes from Xenophon and Shakespeare as chapter headings is not an allegory. In reality, that’s the sort of depth one should hope to get from good fiction. It’s not an allegory, but when fiction is done well it explores the depth of the soul. Which makes it hard to not feel like it’s saying something very deep.
I love that Adams composed the book as a story for his children on long car rides. And I love that when writing his story down he became good friends with R. M. Lockley, the author of The Private Life of the Rabbit.