One of the most powerful humans, yes, mortals...there's the high elves, not encountered yet in the VN. And Athagan, that would mop the floor with the MC in seconds. Even Sariel, and Roger, would beat him. They are old, cunning warriors with more tricks in their sleeves that hair on their heads. And dragons. And some other indiividual, some hostiles...
As far as the Crown, no, it is not bestowed to the Aetas Dynasty by any Gods. But, like said before, nobles are nobles...they want to hog the power to themselves. Not all of them, some are genuinely good people that wish the best for their subjects, like Athagan. But some of them are scheming assholes. And other just want to seize the power they can to protect their own in a slowly dying world .
And the MC, well...it's not explicitely stated, but...come on. He's not the type of guy to want to be behind a desk all day long pushing paperwork. And, he genuinely don't care for titles, except for what advantages they provide. And the advantage of being a King come with so much responsablilities... And look how it impacted Sariel life. No, he don't want any of that shit, he's far better off as the heir of Wildale from his POV.