First, I would condense most of the Upper Planes into one "Heaven" plane. It could be called basically anything, from just "Heaven", to "Mount Celestia", or "Elysium", but for now we'll just call it "Heaven". I don't like how the Great Wheel will separate the afterlives of even good creatures from each other (so family members will be split up if they're of different good alignments), and think that one heaven could just fit all. It could have different layers (possibly one for each type of good alignment; chaotic, neutral, and lawful, but I'd prefer if the sub-divisions of the plane were more like home-realms for Angels, Archons, and Couatls, or something like that, but perhaps both of those could be used in the same setting). The plane is pretty simple; it would be Heaven. A paradise. A place that you probably never want to leave if you come here, with amazing weather, endless food and drink (maybe Nectar and Ambrosia), friendly people, eternal celestial servants, and so on. The Gods might live here if this cosmology has explicitly real gods and they're stated to live in places that the setting's characters can access, but this isn't necessary (maybe take a note from Exandria and have the Gods be real and present, but they can't journey to or interfere with the mortal plane). Either way, Celestial Paragons (Archangels, super powerful Couatls, possibly called Quetzalcouatls, and Head Archons) would be in charge of running most of the business on the plane, and would be what Celestial-Patron Warlocks would make pacts with.
Second, I would also condense most of the Lower Planes into one "Hell" plane. Again, the name doesn't really matter, it could be "Hades", "Hel(l)", "the Abyss/Nine Hells/Acheron/Pandemonium", or something like that, but it would be Hell, the home plane of Fiends and where people who do evil get sent when they die. I personally would probably use
my previous idea of it having 7 layers, each attached to one of the Seven Deadly Sins (with an Archfiend that embodies one of the sins ruling each level, like Mammon for Greed, Yeenoghu for Gluttony, Baphomet for Wrath, etc), and probably have the Blood War just take place on this single plane of existence, but that isn't necessary to this idea. Also like the Heaven plane in this same cosmology, the evil gods may or may not live here, it depends on the setting's deity situation, but the Archfiends definitely would, and would be what most Fiend Warlocks make pacts with.
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