Eh the whole "my SW is smarter" is just no.
While my SW does spare Quinn it's because he's a resource, useful and they feel that the only one they'd betrayed him to is Baras he still should be killable. (It'd make my choice to save him matter more too.
) The devs let the SW get rid of useful things to him/her before that as well (that said if Quinn is killable Jaesa and Vette should be as well. Especially Vette. By god is she annoying). The SW destroying things after he/she feels they are no longer of use is a running theme. I don't know why it's averted with companions. Oh wait yes I do. The whole "oh noes I actually killed mai companion?!?" bleh.
TLDR companions should be killable or dismissable after they've outlived their usefulness. My DS SW dragging around Vette's wisecracking self when he's killed people for less is *** inducing as I'm sure some DS SW killing people for treason keeping Quinn around is *** inducing.