@Latecomer
Tirek had Discord directly protecting him in Twilight’s Kingdom, which if Discord
wasn’t behind everything, probably means he’d get stomped into oblivion, fast. The only reason that he didn’t get hunted down and stomped was because of Discord, since Celestia said as much.
He can’t mind-control anyone to our knowledge, and there’s only one of him.
As for Cozy Glow, I’m not quite sure if she could pull a direct repeat of S8, considering that those magical artifacts may or may not have been damaged or destroyed in the process of that explosion of magic. (I don’t
think we’ve seen them since, have we?)
Chrysalis would obviously be damned to fail if she tried alone. She can’t just slit their throats in their sleep one-by-one, because that’s probably not extravagant enough of a revenge scheme for her.
If Sombra brought them together, then I think they would’ve still needed an artifact to help, maybe.
Then again, mind-controlled slaves do help…