I mean, he is among the most powerful outside of the First Ones and Azeroth rn…
But like you said, he isn’t among the final bosses at all. Hell he is but the starting point of a new age for WoW. Sargeras May return and face us at Zereth Ordos at the Clocktower of the First Ones or something like that lol
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Or the Demons took bodies from Zereth Ordos or even Zereth Tumult and became a chaos God esc thing, but like the Chaos Gods, they are at war with eachother or have multiples layered realms within the Nether, one transcending the other through a high outer range/expanse