He's Satan! You know, the ultimate bad guy, the one who tempts men to commit sin. It's not an unheard of theory in that Chernabog is literally this in the animated Disney canon, influencing the actions of all other villains. In fact there's even a series of novels called The Kingdom Keepers where he's the biggest threat amongst other villains & supposedly he'll be in the sequel to the live action Scorcerer's Apprentice, having been left out of the 1st movie because the writers thought a cameo doesn't do the character justice. So there's definitely the opinion among Disney's staff that he's a big deal.
Now how exactly does that translate to KH mythos? Well what causes people to do bad things in this series? That's right, the darkness. So running through the math: Chernabog=the Devil=Influences others to evil=the darkness, ergo Chernabog=Darkness incarnate.
Also, just look at him & then look at shadow heartless & tell me you don't see the resemblance. Black skin, glowing yellow eyes, one could mistake him for a really heartless. That he appears only in a heartless controlled world & has no journal entry raises suspicion that there's more to him than we were let on.
All of that led to me getting the idea Chernabog was some sort of alpha heartless, the original master of all heartless. Red eyes+no chance of a Mickey in RoD game now+lack of english voice overs pretty much shutting down the possibility of NA DLC release=MAtgSy being a tad bit grumpy lately.
Your expecting the "dark force" to have a personality? I think that kinda goes against the idea of a force of nature type antagonist.