Client wants .story (unpublished files) - do they need this?

The point about the camera is valid.

Face it, if the client is good enough at design and creation, and nefarious enough in intent to want to use your design to steal your business, they are good enough and nefarious enough to steal it by looking at your finished product.

They hired you because they can't or don't want to do this sort of thing; after all, they have a business to run.

When I was much younger, I did some opinion writing for newspapers. My biggest worry starting off was that editors would change my output and maybe make it say things I didn't say. An editor who was also a friend laughed at me. His point was that the last thing the editor wanted was more of that kind of work, any editor that has that kind of time and inclination will write the pieces himself.

That said, if it is as much work for them to get a product from you, and in the end it looks like something they would have done, then yes, they probably don't need you.

There is something to be said about being good enough to make it look easy, but in the end Phil is right. When they look at your product, they need to say "We couldn't do that," or  "We couldn't do that that fast," or "We couldn't do that that well." Those are the reasons they hired you in the first place, and if you prove them correct in that original assessment, your work is safe.