Except with Hiw to Train Your Dragon they were never trying to adapt the books. They looked at the books, and decided to do their own thing, barely drawing on the books. Which, personally, is kinda great. You have this fantastic world and story in the books, which they didn't butcher. Instead creating a new, unrelated world, which is still quite good.
I am unfamiliar with these Warrior Cats, but would you rather see the books adapted poorly, or scrapped for a more original interpretation?