They essentially function the same way. As in Kale, Broly, and Freeza are all equally freaks of nature that were born with tremendous power. The label "Demon" could be more metaphorical in this case, and if not it could possibly mean they all have the potential to become a demon (Freeza pretty much is for all intents and purposes).
it never really made sense that there were legends about Super Saiyans and THE Super Saiyan
Less sense now that SSG is part of the Legend