We'll have to agree to disagree then. While you aren't wrong, there is an argument for the other side, too. Neville is still a legend, at the end of the film, so it does not change the entire meaning of the title. It's just that the film's example of a legend was not the same as the novel's.
On a related note, the way I judge a book-to-film adaptation on it's own merit (regardless of the novel it was adapted from) is mainly because of The Shining. The novel and the film had it's many differences. Stephen King, the author, didn't even like it. However, it was a damn good film, and I'll be damned if I say that I dislike a film just because it wasn't truthful to the source material. That is why I judge the novel, then separately judge the film that it was based off of. The same goes to the Harry Potter books and films. Harry Potter & The Prisoner of Azkaban was probably the least faithful adaptation so far, but it is my favorite movie of the entire franchise. I'll be damned if I disregard how good that film is because it wasn't faithful to it's source material. No personal preferences, just valid criticisms.
That's just me...