2 possible explanations with the recent retcons here:
The agents of the Source include the Archangels and are above Perpetua.
The Dimensional retcon puts them far above the multiverse and that includes Heaven in Morrison's map.
We haven't gotten clarity at least based on my [limited] research. So either could be correct.
However, putting aside the whole dimensional shenanigans (that Snyder uses to cover up his inability to write credible threats), WF is on par with Base Anti-Monitor. And Base Anti-Monitor - retcons in place - hasn't done near enough for me anyway to compare to Michael. Basically, is being a dimensional plane above enough to bridge gaps in power? Had everything been switched over to have all happened from the 4th Dimension...
Mind you I combine Vertigo Michael with DC Mike, so I dunno. Could be way off base. Haven't even read the other Vertigo series aside from the Original run.