Jia Yan's control over his subordinates was actually done in a situation where both parties were aware.
When Jia Yan handed over his cultivation system, he never considered abandoning this group of people, and he was sure to personally take action to kill them if they intended to betray him.
With regard to the Yin Yang system he created, Jia Yan completely understood how terrifying its future potential would be, so he wouldn't even allow the slightest chance of leakage.
Of course, Jia Yan didn't know yet that certain elements and insights within the Yin Yang system needed to come to Jia Yan's side to sense his power for promotion. If he knew, then he wouldn't mind letting his subordinates leave.
Because without a way to advance, even if others learned the Yin Yang system, they couldn't promote, nor could they decipher it, which made it safe and worry-free.
However, Jia Yan wouldn't give up control over his subordinates just because of this.
