I think it's perfectly reasonable to concentrate criticism on the Sun/serial killer sub-plot. First, because this is what the series' creators chose to focus on this season, this is their final big "what we have to say". Second because it is, quite clearly, a weak and flawed story which does not meet the extremely high standards "The wire" has taught us to expect.
I undestood what bothers me about this story during the scene where the Sun staff moan about not being invited to the prep-walk Bond organized for Clay Davis at the steps of the court house. "Today all they care about is the video" says Gus.
So if the newspaper has become, or is becoming, irrelevant in the media world, why is it the sole star of David Simon's treatment of the media's role in the decline of the american empire ?
We don't get the whole story on "The Wire", but we always get the most telling story, stories that feel essential. Like the port workers who told the story of Labour, like the four kids who told the story of education. The newspaper isn't that. It seems the sun has been chosen to star for the wrong reasons: David Simon's strong personal feelings about journalism and his former paper.
I think "The Wire" creators are guilty of the sin of Hybris, and in true greek tragedy style they shall pay for their sin. I'm not so good with English Literature, so I don't have a matching Dickens reference.