I've watched this thread grow over the course of a few days and I'm always surprised as how invested people are in lore that is pretty superficial and has been more or less since the start.
Like... what was the actual story of Vanilla? What felt like the biggest parts of the story were in the raids. So either Zul'gurub, Ahn'qiraj, Blackrock or Naxx. They're all focusing on a small thing that a faction is making big for x/y/z reason. Dark Iron dwarves summoning the fire lord, Gurubashi summoning Hakkar, Cthun trying to take over Azeroth. Kel'thuzad taking stuff over.
It's not some grand, interesting motivation really. It's nearly always bad guy does bad thing because bad. The only difference is that each expansion does it over the course of the whole expansion, not in small bits that are countering each other (for the most part. I know there were some opposing bits like Firelands in Cata).
So in terms of following/forsaking lore, I personally see it as highly likely that each faction, even the bright shiny factions like the draenei/lightforged would have the odd person who goes "hmm, that seems like a good avenue to help my people, sure let's go."
As much as I enjoy the story put down in WoW, it's not exactly high-brow, super in depth stuff like Lord of the Rings or ASOIAF. It's the fantasy equivalent of Marvel. We watch a cool guy do a cool thing against a bad guy doing a bad thing, and I'm here for it. And if that means I also get to play something like a lightforged draenei who weirdly loves demons, then I'm in. That's also my primary reason for loving D&D. It allows for daft combos that you warp and twist to make fit.
There's the odd nuanced bit of storytelling here and there, and I love those moments too, but when push comes to shove, WoW lore is extremely broad and it will probably be that way forever because it's much easier to sell a story of big bag guy shouting "You are not prepared" than it is to do a 30-quest chain of a lightforged draenei questioning his identity to become a warlock before you've even started the character, especially when it's a small fragment of an entire pool of choices that won't get picked that often.