The Balrog vs The Witch King

[obloquy]

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.

Again, it has nothing to do with actual status and everything to do with perceived status. Yes, the Witch-King had commanded armies (and even held a kingdom) before. In LotR, there is a very obvious transformation taking place from his more or less anonymity among the Nine early on, to his unveiled military leadership on the Pelennor. This transformation does not require any literal power-ups; it's perfectly congruent without them. In fact, your own point that the Witch-King was an accomplished military general before his role in LotR argues against the necessity of a literal enhancement.

Originally Posted by Raynor

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.

Are you saying that because he used the word "demonic," he must be referencing Sauron's nature as a "demon," and therefore the "demonic force" was bestowed by Sauron? I think the word is perfectly applicable without such a connection.