Another myth is that Sylvanas started using mind-control in BfA with Derek. It's not, she was already mind-controlling undead as far back as Cataclysm. Evidence is Invasion of Gilneas and Battle of Andorhal, where ex-Alliance soldiers started yelling Forsaken war cries upon being raised.
If anything, what is surprising is that people like Voss started being shocked by this only when she raised Derek. Did Voss not hear what Sylvanas was doing in Andorhal?