Have to agree here. One of the things I dislike about LoS is Satan even being involved at all. Heck, I dislike/love Zobak so much more as the villain in this. I constantly want to face punch him and he's so manipulative. He's the one person I want Gabe to actually get some kind of revenge on.
The way I see it, Zobek is the real villain. It's his quest for power that fuels the whole story. While Satan may have come up with Zobek's plan to unite the God Mask, Satan wouldn't have had anyone to execute it without Zobek.
Satan, on the other hand, is the vehicle. It's his power that serves as a threat to move the story along, because honestly, who serves as a threat to Death and Dracula other than Satan? At the same time, while he has the power, he's not the one who holds all the cards. He didn't possess the Devil Mask, he doesn't have the Vampire Killer, he isn't using Dracula's power to achieve his own aims.
So yeah, while Satan is the final boss, I don't think he's the real villain. He's more the "threat".