>>533602465
Doomsday device is hypebole but Vancleef and the Defias were genuinely planning to kill everyone in Stormwind not just the nobles.
Blizzard probably wrote them that way so the Defias can be easily accepted as evil by the players and so they won't sympathise with them, like when a villain in a show/movie is making a strong arguement for his actions and then the next scene the villain stomps on a baby.