You got that right. Nice to be remembered.
Actually, it was that and every other alteration of the Beyonder's origin since he first appeared.
He started out as the most powerful being, with even the Living Tribunal being considered less powerful in comparison, but then Bryne, who disliked and mocked everything Shooter had ever done, changed the origin to make the Beyonder weaker and saying he was a mere piece of a cosmic cube.
And now there's this mutant Inhuman thing.
Next, it'll be revealed he's actually just some guy who pretends he's really powerful by using hollywood-type gizmo's and he's Quintin Beck's younger brother.

An Inhuman mutant! I remembered when I first saw that carp at the bookstore. And since he was an Inhuman that meant that Black Bolt was his king so he had to obey his king. I wouldn't use that book to wrap fish in only because they might turn into mutant Inhuman fish that can change history if they swim fast enough.

Well, only if they swim fast enough in the opposite direction of the Earth's spin on it's axis and even then, only if they were trying to save Margot Kidder.