The material I've quoted - from rulebooks, modules, etc - has shown that from the earliest days of the game, there were clerics using spells granted by demons and devils.Permerton's rules, from what I've seen of them (which isn't every post), don't really support your assertion. And you haven't provided any facts that I've seen.
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But the fact bot arch-things and gods can grant spells doesn't make them redundant.
Upthread you denied that, agreeing with @Maxperson and @Helldritch that the game rules went the other way. Now you seem to have changed your mind based on your discovery in the 5e DMG of exactly the same thing as I've been pointing to in earlier works.
I'm not clear what lingering doubts you have about the material that I've quoted.