Valindra is variant on a lich with some of her own stuff, but is about as strong and is the same CR.
Sammaster is a bit more powerful and also has some of his own stuff, but has one major gimmick.
I think you are misrepresenting Grym a bit, he’s more of a puzzle boss, who will take large amounts of damage when the parties position him right.
BG 3 Monsters also don’t have 5e Legendary Resistance or Legendary Actions.
They showed the Psion a while back asked for feedback about a week later, then yesterday they released a version based on the feedback they got for the class. The same thing happened with a bunch of their playtest stuff.
Just because feedback can be given after a fairly short period doesn’t mean...