I see no difference in her leaving Bolvar alive to her randomly saying the horde is nothing and abandoning her position as Warchief. She doesn't care. She's focused on one thing w/e her goal is. She went in there to destroy the helm. I just don't get why her leaving Bolvar alive is some massive mistake on the writers. Sounds more like some people didn't like that outcome which is fine but to wantonly attribute to bad writing makes little sense to me.
I just see the constant theme of people using the "bad writing" throwaway line interchangeably with "i don't like the writing". It's ok not to like the writing or parts of or all of it but don't pretend like your taste determines what is or isn't good/bad writing.