The concept of Bad Guys above the old gods is pretty silly to me. The old gods were created to be this inscrutable force of malice unbound by human logic, like their Lovecraftian inspirations. It's just very obviously a retcon they made because if we're finally gonna put an end to the Burning Legion (and lord knows it's about time they go away proper-like), we need some new big-picture villains, stat.
I mean, the Void Lords are basically so fucking strong that we probably will never face them, ever. Sargeras was so scared that he decided it's better to destroy and remake the whole universe instead of there being even the sliver of a chance that these things can manifest in our realm. But they are just this looming evil in the background that is there.