Speaking to the frustration in these posts and the veering away from realism in the show this season towards its more didactic, soap-operatic, parody-like tone, I think it's a case of writers rushing to an ending for their story. I think that apart from the social commentary of the show, which is obviously very pessimistic and open to question, its main virtue is that is has consistently presented a complex social place and a host of characters in an incredibly vivid and realistic light. It's introduced to viewers the foreign cities within American cities and has made the characters we dismiss as marginals and criminals compelling.

To venture interpretation of this season I think one needs to look back to season three. There, the idea was that reformers in the system can't succeed. The inhuman social forces, and the ruthless characters (i.e. Marlow) who master these forces, and the personal ambitions and trade-offs that the system forces on ambitious reformers (i.e. the the Mayor, Carcetti) doom reformers to failure or to betray their ideals. This season, the outlaws, or renegade, rugged, individualistic characters fully break from the institutions and try to reform them by manipulation. I don't think this excuses the loss of quality realism and compelling character narratives, but it at least explains the commentary of the show. The institutions are broken, and they eventually break the most capable people. If the people turn cynical or desperate, they abandon institutions and finally, desperately, try to manipulate them. In this light, Bunk is jaded and the narrative is stacked against him, but at least he isn't willing to compromise his principles (even Omar has betrayed his promise to Bunk). So the fight isn't between Omar and Marlow in the show's moral universe, it's between Marlow and Bunk. Omar and Marlow will probably have the penultimate duel.

Add in the newspaper as the embodiment of outsiders trying to hold the institutions to account, the institutional soul of outsider reformers. The institutions at the center are broken and they break people. The institutions on the outside, the watchdogs, are atrophying, failing to notice important stories, and even corrupting and breaking their own members (Stephen Glass Templeton). The ultimate message might be that news cycle coverage and focused sociology and reporting works on shining the burning limelight on peripheral issues, or maybe issues in isolation of their full context and distorts and narrows, and ultimately destroys reform and the full, comprehensive, panoramic understanding of the modern condition that would necessarily precede this reform. It's perhaps ironic that the show has sacrificed its telling of a complicated, realistic and representative narrative for the sake of being didactic.