Also, uh, Garithos wasn’t mind controlled, he was never mind controlled. He was just a bad guy, but the problem was everyone else higher ranking than him was dead, so he yoinked the title of ‘Supreme Alliance Commander’ for himself, and no one could really say it wasn’t his by right, because there wasn’t anyone of higher rank. Also, he was a human supremacist, he didn’t just hate elves, he also had a major disdain for dwarves.
Blood Elves as they were in BC completely fit in with the Horde, even if the way they got there was a bit contrived. Sure they look pretty, but in BC they were the embittered survivors of their race, living in the ruins of their kingdom, stealing mana off things, and basically letting the weak of their society, the Wretched, go off and live in squalor and kill them if they got out of line. Seriously, when they were brought into WoW they were second only to Forsaken in terms of the questionable morality ladder, they fit perfectly.
Of course then Blizzard fixed the Sunwell by the end of the expansion and they slowly morphed into High Elves with a different name but… yeah.