WoW’s storytelling isn’t arithmetic, it’s algebra.
You don’t add Existing Fact + Existing Fact to produce a Story Event.
You Start with some facts, AND the event you want, and you solve for whatever additional facts need to be introduced to get you there.
It’s not “1 + 2 = X”, it’s “1 + X = 5.”
The Horde will be evil if Blizzards wants to tell another Horde Evil story. The current state of their leadership is irrelevant. Likewise, absolutely nothing about the Horde prior to BfA mandated BfA. A different leadership group would have changed the variables, but it would have done absolutely nothing to prevent the solution that Blizzard was shooting for.