Actually design is strongly protected while direction is not.
Loy Acernas had already brought suit against the Caldwell Theater for copying his L!V!C! design before Mantello did for direction. And his was the easier case because there is precedent for design and choreography being covered by intellectual property law, while direction is not.
I think you oversimplify design by seeing it as just the number of doors and the room the scene takes place in. Even within those guidelines, there is much work that needs to be done.