The Wire really is a remarkable show in that, unlike a most of TV before it, it literally springs from who the characters are. The closest thing to an imposed narrative is the decision to focus on a specific segment of the phenomenon that is Baltimore, the police bureaucracy in S1, the white+ working class (well before DJT) in S2, etc. Literally everything else derives from the who the characters are, not the arc imposed by the writers. The scripts are as much channeled as written.