I'm guessing you're asking this: How powerful is Darkness? It is shown to affect people, but does it cause any real fatal effects? Is darkness powerful enough to destroy a large robot?
Well yes and no. In Kingdom Hearts: Re:Chain of Memories, Riku uses a slight, called Dark Firaga, in which Darkness is shot out of Riku's hand. This is a form of Darkness, but is not straight up "Darkness." The idea of Darkness in Kingdom Hearts is personification, giving human characteristics to something abstract. The very idea of Darkness is Abstract. So can Darkness destroy a large robot? Probably not. Can a form of Darkness destroy a large robot? Yes.