There is an insta-kill option for Dror, Minthara, the Hag, Phase Spider in the form of an easy bonus action shove with or without invisibility. It feels like Larian put this LOLIWIN cheese feature into the game and basically set up every important fight with the enticement of it being readily available.
The knockback arrows and ability to freely shove like this is clearly intended by some (humorous) design for Larian to create what they consider essential moments in the game.
I really hope there isn't always some such mechanic conveniently placed in every fight, just like this high ground advantage and backstab mess.
Honestly, with all the crying and yelling by certain "game journalists", they probably did this on purpose to cater to that "I just want story, not to actually be a game" crowd. It is there, you can do it, but you can also ignore it and do the fight the way it is meant to be done.
