Pretty good summation.Mechagnomes bad because "Alliance didn't want it".
Mag'har good because "Horde wanted it".
End of story. Stop pretending as though there is any other reason for it.
Ironically, nobody asked for the Iron Horde to be playable, but because you can play pretend that your marking-less, boring Warsong/Frostwolf orc is from Outlands nobody cares.
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Something that particularly infuriates me is that you KNOW that people will say "Horde asked for Vulpera and they got them" when Vulpera were designed to be playable as early as late-Alpha. They were always going to be playable the moment they got those new models. Nobody cared about them when they looked Cata Goblins without tails.
Doesn't matter though. People will say anything to further their shitty little narratives.