Is Magnus and the Magna Ge the most powerful gods currently? more powerful than the Daedric Princes and the Divines? not counting Padomay and Anu of course they are the force of the universe rather than gods.

Well, "power" is a difficult thing to quantify, but I'll try...

I think they are the least powerful in all useful definitions, because they have no connection to Nirn. Magnus and the Star Orphans fled the Mundus at convention and no longer participate in it - although the constellations do affect mortals, they do not appear to have any willpower, agency or sense of self as other gods do. Magnus is revered merely as the opening to the source of magic rather than its creator or giver. The mortal perspective of divine power is the only one from which we can really discuss things, and from that view, the Magne Ge are powerless due to their irrelevance.

Why would they bother to flee then? Why wouldn't they have agency?

Look at all that creatia...