A film composer will compose better if the material given to work upon is powerful in the first place. Comparing Kung Fu Panda and How to Train Your Dragon, for example--I do think HTTYD was the better movie of the two--better concept, better ending, better character development...and naturally, the soundtrack went a lot better with the scenes, even though KFP's was very melodically appealing. Plus, it was so much more moving, and so's the soundtrack.
If you can feel the film, inspiration comes more easily. That's why I think your fame as a composer depends on opportunity and not on talent. Being with a job in which you obligatorily ride the work of another, the quality and recognition of what you do really depends on that person whose work you build upon, your unspoken decider-of-fate in a sense. Similar is game music composing; it's about the images and feeling them, and relating to a world that another has created.
Still, this sort of job is the kind that's inextricably linked with another's story, another's fantasy, another's heart...and that, I think, is one of the most amazing feelings in the world.
Just a thought.
