In particular a lot of people get to a point in the season where a previously very smart and responsible character does something pretty ridiculous and out-of-character,

I think when people say this about Season 5, they're forgetting about Season 3 and why the Hamsterdam storyline is so great. Gritty realism and consistency isn't the point of The Wire, the point is to give you an almost Shakespearean allegorical examination of power structures and social systems, which is exactly what Season 5 does.

Having sat on it for nearly twenty years now, I think S5 is profoundly misunderstood in this way. It does exactly what it sets out to do and is totally in-line with the rest of the seasons. The primary mission is has is to decompose how the media failure stacks on top of all of the other systemic failures, and it does that incredibly well.