Film is a director's medium, TV is a writer's medium. Directors have very little power in TV, unless they are directing the pilot, which creates the tone and aesthetic for a series. Pilot directors are there through the development process with the showrunner to bring the series to life, which is why most pilot directors often get producer credits as well. Otherwise, most TV directors are following a "tone bible" that they stick to for directing episodes. There are exceptions, when directors really make their mark with stylistic choices (like Miguel Sapochnik on Game of Thrones, or Rian Johnson on Breaking Bad), but they are not the general rule.
In TV, the writer is king. And the showrunner is the head writer and executive producer. They may not write many (if any) individual episodes, but all the story decisions and creative choices go through them, and they get the final say on the story's direction, for each episode and the season as a whole. So yes, most of the blame or credit should go to them, as the individual episode writers are following their lead.