Just because there is a structure does not mean it's all derivative. The idea is that the story lives on top of the structure. It isn't the structure itself. I see people citing movies like "Back to the Future" as examples that do not follow this structure. It does. Almost everything does. I took classes at one of these types of places for about two years. One thing we used to do was analyze films and try to find their structure. Amazingly, even the most seemingly unstructured movies followed the three act structure. There are exceptions, but they are rare. One notable exception might be the movie "I am curious yellow." But it's also highly experimental.
Or to put it another way: structure is the bones, story is the skin.