Ok, let's see if I can get my point across without ruffling too many feathers.
Like many here, I've been gaming a long time. I've played 7 different iterations of D&D from Moldvay Basic/Expert up to 5e now. So, when you talk about lore in the game, my first question has to be, "what lore"?
In my time in the game the following statements have ALL been true:
- There are no demons or devils in the game (Moldvay Basic/Expert, Core 2e)
- There are demons in the game that live in the Abyss (1e)
- There are demons and devils in the game that all serve in some eternal war against each other, but, aren't called demons and devils (later 2e, 3e and 5e)
- There are demons and devils in the game but have an entirely different back story (4e)
So, tell me, definitively, are there demons and devils in D&D an what is their background lore? At BEST you can claim canon in a single edition, but, even then, that's not true. I've got, on my shelves right now, THREE separate, distinct write-ups for a 1e Lolth. Fiend Folio, Queen of the Demonweb Pits and Lolth as a goddess (Dieties and Demigods).
Better yet, I started D&D in Moldvay. One of the first adventures we played was Isle of Dread. So, tell me, where is the Isle of Dread? It's been in Mystara, Greyhawk and a demi-plane as far as I know. So, which is it? What's the lore?
D&D lore has been mutable since day one. Daemons morphed into Yugoloths which later morphed into something else again. Kobolds went from little dog people to little lizard people to being tied to dragons and having a draconic heritage. On and on and on. Paladins went from Dudley Do-Right LG exemplars to a character of any alignment that reveres some sort of divine aspect. How is a 5e Paladin even comparable in lore to a 1e Paladin?
Lore CHANGES. Lore changes all the freaking time.
There is no "D&D Lore". Or, at least, EXTREMELY little of it. The game has folded, spindled and mauled "canon" so many times that you can basically find evidence of "canon" material for any position you like.
Like I said, you cannot actually definitively answer any of the questions I've asked in this post. Your answer will be completely different depending on what the date is. We have an evil Paladin in our War of the Lance Dragonlance game. Good grief, how is that even REMOTELY canon. War of the Lance era Dragonlance has no paladins AT ALL, for one, and certainly not evil ones, which didn't even exist in the game at the time. The aforementioned wild mage gnome is only possible through ret-cons to the setting. FFS, we had a kender cleric at the beginning of that campaign!
And no one batted an eye. No one said the slightest thing. No one cared. Because no one actually gives a rat's petoot about canon. If canon actually mattered, then none of these things in this post would happen. But, canon isn't important. No one actually cares about it.
Until such time as it becomes convenient to care about it. If CANON was important, then all changes would be important. After all, you can't claim canon is important when virtually every single aspect of the game changes, and often changes radically, year after year after year, edition after edition, and most of the changes are perfectly acceptable and many of them are applauded. You can't claim the importance of canon when it's convenient. It's either important or it's not. If changing elves to eladrin is bad because of canon, then so is EVERY other change. Now, if changing elves to eladrin is bad because it makes the race unfunny, or unplayable or some other reason, fair enough. We can talk about that. But, if changing elves to eladrin is bad because change is bad, then you can't then ignore all the other changes just because you happen to LIKE those changes.
If change is bad, then it is bad. But, you can't try to claim change as bad only when it's convenient.