I think you're thinking of the wrong factoid. The retcon was that the Eredar corrupted Sargeras, rather than the other way around. In warcraft 3 what we now know as broken draenei say the Eredar caused their decline, but that's not necessarily mean they weren't part of the same race. But at that point we enter a nebulous lore territory, because two separate teams were writing Warcraft 3 and Vanilla WoW. I don't think the Draenei were even mentioned in Vanilla WoW, just like the history of the world in Warcraft 3 never mentions the Dragonflights.
It's funny that people think Metzen is going to make Warcraft less-cosmic, when he's the one who came up with the all the stuff about space-travel & sentient rocks.Big Talia Fordragon Energy. The first rule of WoW writing is just because a character takes up hours of gameplay doesn't mean she's ever going to do anything important.