The Great Darkness as it were refered to when it existed in the 80's where in Vertigo, thuss 50% of Yahweh is now.
It's the paradox, if God truley was omnipotent and truley good, why did he create the devil, Satan, why did he create evil?
So God in Vertigo is now both good and evil, two sides merged.
But Yahweh is not supreme as he stated in Lucifer #70, after he merged with the Great Darkness that is.
But Presence is, and the Brothers where to represent all that is in both universes, the supreme beings, the once which's manifastation was everything.
As they said all individual's were unique, that atom will always be that atom, nothing else will ever "be" that atom.
But there were two beings who were exactly the same.
The Brothers, they were the same, they couldent exist with their lack of uniqueness. - It's a paradox, therefore their fight, two omnipotents, it couldent exist in the asme verse, they ended up splitting it.
So they both could stay unique.