Vlaakith is both extremely powerful and not powerful enough. She's more than a lich but not much more than a demigod.
Myrkul, Mystra, Jergal etc have real power so have no need to act so directly, preferring to use intermediaries and sucking up their defeats as just another Tuesday like timeless immortals do.
Vlaakith actually uses Wish, and I suspect she's still subject to the risk and drain associated with it. But does so because she's so emotional.
It did seem a bit silly my paladin obviously lying to her to assuage her and lae'zel. And no fall from grace for such deceit. Oh well, it's a big video game, can have reactivity to every single line of dialogue.
