[Raynor]

I believe there is "reasonable doubt" about this interpretation. The nazgul are already described to the reader in superlatives, be they regarding power or hierarchy. The witch-king is described in the prologue as a powerful and successful leader of armies, Bombadil refers to that too and Gandalf says that Sauron governed Mordor through the nazgul. Moreover, the very wording of "added demonic power" in the context of simply reader perception concerning his role seems somewhat ... uncalled for. Imposing, majestic, frightening or other adjectives might justify this interpretation, but demonic not, imo.