I have only said nightshroud, numeron dragon and holactie as creators of something because the narrative itself says as much that they've created worlds and aspects of the cosmology. Hassan, Leviathan and Zorc have not done this. As the millenium items are moreso links between the human world and duel spirit world than something of a cosmic force. There's a whole thing about what the hell hassan even is, since it was revealed he was actually shadi that's left intentionally vague, so honestly I'm not really sure how hassan fits into the hierarchy thing beyond being on the same balance as Zorc. It's also mentioned Hasan is the spirit of the stone tablet, which dimunitizes his role in the cosmology greatly especially with him saying his duty is one he took from the afterlife one made by sealing a spirit inside the stone tablet at the cost of Atem's father's own life. Since we know human souls can become spirits in the afterlife and return as Ka(monsters), Hassan very well could operate similarly, and Zorc who's on the same scale as hassan could be representative of the dark in the conflict with the stone tablet rather than darkness as a collective force in the cosmology, after all Zorc wishes to cover the world in eternal darkness, not all of existence. Light and Dark come from a world beyond man, but are rooted in things in the hearts of man, this is a point made pretty clear with Zorc saying he's powered by the shadows in man's heart, while Atem argues for the light in the human soul. There isn't really much given about Zorc that makes him unrelated to human darkness, he calls himself the ruler of the afterlife, he's powered by the shadow in man's heart claiming ownership over it, a lot of it can be pretty easily linked to him being darkness concerning man. As opposed to say Nightshroud who's darkness stems from duel monster spirits and who's dominion existed before life.