@Suzaku

Yes, they do change things over time. But the RPG books are still in the category of what Blizzard considers "canon", so until something officially says, "We've decided to change the lore on the Well and how arcane energy is corrupting," I'm sticking with it. And fel energy has the additional complication of demonic components, so I doubt there's any way it could be non-corrupting. It being the most corruptive makes perfect sense.

Having played mages and warlocks, I know what your character learns about arcane energy and how it corrupts. I think what's happening is they're misguided... even the teachers are misguided. If the high elves taught it to others the way they were doing it, and they were doing it that way even when they were still night elves, and they've never had that, "Hey! We've been doing this the wrong way!" lightbulb go off, then of course arcanists will think it's just naturally corruptive. They have no other information to go on.

Similarly, look at the "Which druids came first? The Tauren or the elves?" question. Both groups think, and teach, that they were the first. A blue post confirmed that the night elves actually were the first. The Tauren are mistaken. In an immersive world like this, in-character information can be, and often is, mistaken and biased. No different than the real world. Somebody needs to call Lord Kelvin and bring him up to date on the real age of the planet and why his heat-death theory doesn't really work out.