These claims may be exaggerations. Book 1 featured one fight between Stanley (Rocking Out) vs. mostly Transylvito units using show tunes. Stanley's side suffered many losses and had to retreat from the hex under the cover of Foolamancy. While this incident does not prove that Dance Fighting is superior to Rocking Out, it does demonstrate that Rocking Out forces are still vulnerable to "less Titanic" opponents.
So far, only the Arkenhammer is known to allow Rocking Out.