really the main difference between the characterization of Sophie and Howl in the movie and Sophie and Howl in the book
is that your average ghibli protagonists are a good-hearted and naive young person who needs to learn to believe in themself and their companion who is both more worldly and more otherworldly but needs to learn to believe in others
and your average diana wynne jones protagonists are little shits. all of them. such little shits.