@Snarf Zagyg get ready for another post complaining about #5, but I'm enjoying it at least! This is the Greyhawk topic nearest to my heart.
Something to consider, which relates directly to the influences of "divinity as mere power," is the notion that various powerful demons and devil are considered lesser deities on their own plane. The only place I've actually seen a mention of the difference between "divine" beings and these fiends is in T1-4, where it mentions Zuggtmoy being jealous of Lolth's "recent ascension," which is an obvious reference to the events prior to Q1. Given that this part of the adventure was not written by Gygax (who originally had Lolth as the primary villain in T1-4), it seems this doesn't mesh with the rest of the setting. Using "divinity" as simply a level of power makes quite a bit of sense in Greyhawk. Hextor and Heironeous would have then been mortal brothers (or possibly brothers-in-arms) born long ago that ascended to immortality together. Greater Gods that have little interest in the affairs of mortals might be that way partially because they were born elsewhere.
One interesting aspect you do not really touch on is the breakdown of the boxed set deities by Greyhawk human ethnicity, so there are Flan gods and Bakluni gods and ones who are both Oeridian and Commonly worshipped and each have an entry in the chart with interesting things like having two gods with very similar portfolios for different pantheons on the same world, such as Boccob the commonly worshipped Greater God of Magic and Arcane Knowledge versus Wee Jas the Suel Greater Goddess of Magic and Death.
And again there is a range of description, some gods have descriptions and stats, while others are just names on a chart with a few details that a group can fill out on their own.
I think Gygax did a great job setting up a multi-cultural polytheistic environment, but I feel the space limitations really did a disservice for the setting. The whole thing is a hot mess that is open to a lot of different interpretations, some of which comes off as contradictory. This is great as a cultural representation, but since the gods of Greyhawk actually exist, this makes for a DM's nightmare if they want to have a working set of divinities. I've been trying to work out a Unified Divine Theory for a long, long time, and I just can't get everything to make sense.
I keep focusing on the disconnect between the ethnic deities and the fact that almost the entirety of the Flanaess is of mixed descent. Having a listing of the original pantheon would make sense, because of the ethnic hold-outs like the Theocracy of the Pale, the Barbarian Peninsula, the Baklunish, and of course the Brotherhood. Instead we have the "Common" pantheon, indicating their wide set of worshipers beyond their ethnic pantheon... when very few people really have much ethnic ties to a single pantheon anyway.
My current take, which is a PITA, is to compare the common ethnic makeup of an area to determine what deities are likely worshiped there. Common pantheon deities are worshiped just about everywhere in addition to those found by ethnicity. If a Common pantheon deity also has an ethnicity, it indicates that it has a higher level of worship in areas with that common ethnic makeup. Unknown pantheon deities are just cults spread sporadically across the Flanaess. Oh, and all of this has to fit within the listed areas of worship from the Boxed Set deity descriptions.
The Old Faith is another PITA, since it (Druidism) was originally supposed to be Animism separate from the deities (per Gygax in a latter interview), but the boxed set specifically mentions druids worshiping Beory, Elhonna, and Obad-Hai. I separated the class from the religion, and decided that "Druid" is a specific title of the Old Faith, and that other druids were called shaman or some other such nature priest titles. The druid class still calls upon the nature spirits, but those worshiping a deity do so through their connection to their deity, rather than directly.
