We even haven't seen Sargeras or any of the Titans of the Pantheon yet. But we have seen some old gods and fought them. In wow, typically the villains that we fight later or last are the most powerful foes. The old god's have a major weakness......they do not work together. Sargeras' BL does, and the Titan Pantheon, too. They outnumber the old god's by a landslide.
But maybe the old god's have something like an overmind or parents, somewhere else in the great dark and beyond.
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while you used D&D terms, i wonder why Sargeras should be Lawful Evil? Cause you got it totally wrong here, he is Chaotic Evil like the old gods. He is a friggin fallen Titan to turn everything the Titans created into chaos, as the Titans are lawful. Sargeras is the Chaos. he can't be lawful evil. Thats the Devil, but he isn't a devil he is more like a demon king, backed up with the high technology knowledge of the Titans. He i super dangerous actually. Of course he must be the main villain. Like a rogue titan from highly civilzied alien race with super powers running rampart.
The old gods are not even on the same team among themselves, btw. Doesn't have something to do with alignment. And i think they are more than just chaotic evil. They are pretty much aliens that infested the planet and hard to understand at all by azeroth natives, however the curse of flesh proably makes this easier for everyone.