We are mostly in agreement about the general picture, but just to keep the conversation going...

I don't think (4) is so trivial or that (4a) and (4b) can be equated. For the first, there are other metaethical theories that I think wouldn't agree with the common content of (4a) and (4b). These include relativism, error theory, Moorean non-naturalism, and perhaps some naive naturalisms ("the good just is pleasure/happiness/etc, end of story").

For the second, I was thinking of (4a) as embedded in the global naturalistic, reductionistic philosophical picture that EY is elaborating and that is broadly accepted in LW, and of (4b) as embedded in the global Scholastic worldview (the most steelmanned version I know of religion). Obviously there are many differences between the two philosophies, both in the conceptual structures used and in very general factual beliefs (which as a Quinean I see as intertwined and inseparable at the most global level). In particular, I intended (4b) to include the claim that this perfect entity embodying morality actually exists as a concrete being (and, implicitly,that it has the other omni-properties attributed to God). Clearly atheists wouldn't agree with any of this.