There is a whole lot about AD&D that goes right past people when they sit down and actually tried to play it. Everyone ignores different sections of the rules and glosses over a great many oddities when they set out to create their own campaigns that fit with how they assume fantasy actually ought to work. For those of us that interpreted the game through a Tolkienish lens with no familiarity with the Elric stories, I think whole swaths of the game came off as strange and even wrong, something to be cleaned up in actual play.
But the alignment system in general and having stats for gods and devils in particular isn’t is crazy as you’d think. AD&D alignment corresponds to entire planes of reality, each peopled with their own strains of monsters and gods. To make these odd game elements awesome in the Moorcockian sense, you really need to make them a central element of your campaign, impacting both the magic system and domain level play. One thing’s certain: the results of this sort of play will not at all be “Tolkienesque”.
But yes, AD&D cosmology and devil lore do come from Stormbringer. When Gygax wrote in the Monster Manual that “it is possible to destroy the material form of a greater devil or duke of Hell, but such creatures can not actually be slain unless encountered and fought in Hell or those lower planes adjacent to it”, he was definitely thinking of this book!
More on all this here:
RETROSPECTIVE: Stormbringer by Michael Moorcock
Tor.com — “When Moorcock has a fleet of ships on the horizon, it’s not just a fleet of ships, its 40,000 undead magic-imbued ships. When Elric finally rescues his beloved, it’s not a mere victim of kidnapping he finds, but rather his wife as a bloated demonic worm monster who throws herself on his sword so as not to live such a tortured existence. When Elric dies—well, he doesn’t really, as the struggle for Eternal Balance never ends.”
The Independent Review — “I’m really tired of reading about Elric of Melnibone, and even more tired of writing about him, so here’s my summary of Stormbringer: not fabulous. It felt much too long, and the demon sword killed far too many of my favourite characters for me to enjoy it. But, in a way, I understand that the series really couldn’t have ended any other way.”
Tor.com — “In the first half, we at least have the gratification of watching Elric rescue his wife, getting not one, but two ‘Did You Just Punch Out Cthulhu?’ moments (one with the aforementioned dead god, and one with no less than three Chaos Dukes, including Elric’s own fickle erstwhile patron, Arioch), and a daring escape from Jagreen Lern’s flagship. But once the deaths start piling up in the second half, the grimness becomes absolutely relentless. Not a single Young Kingdom can resist the conquest of Chaos and each is absorbed into its terrifying, seething mass.”
Grognardia — “What made Stormbringer so special to me, I think, was not its rules — though I do think that Basic Roleplaying is well suited to Moorcockian pulp fantasy, moreso than to RuneQuest in my opinion — but the sense it conveyed, just asCall of Cthulhu did, that, though based on someone else’s world, that world now belonged to you. I can’t quite put my finger on how and why the game achieved this, but it did so effectively and that’s why I still pine for the chance to play it after all these decades. Stormbringer is a rare RPG whose succinct, elegant rules feel complete and whose setting feels gloriously incomplete, demanding that the referee and players fill in the blank spaces with their own creations.”