It still requires some text for explanation, so here goes. I imagine a well-balanced show to be circular. Everything fits best in a circle; they're the most efficient use of space. Most shows have an efficient premise, but as they add characters, cliffhangers, history, and continuity, they start getting ungainly. The mythology takes over from the storytelling. It looks like this:
It's a mess. There's no plan, things get lost, forgotten, ignored, or worst of all, lose their impact because they get cut out of the story, by retcons or resurrections or whatever. This could be a chart for The X-Files or Battlestar Galactica, or it could be Angel or Buffy. The difference between the former and the Whedon shows is that the Whedon shows remembered character came before plot. Angel, especially, shifted into emotional resolution more than plot resolution after its excess of serialization in its 4th season caused problems.
The Wire is ruthless in focusing on the important parts of the story for each season, occasionally bypassing formerly important characters and bringing in entirely new ones. The tonal whiplash as it makes these changes can make seasonal transitions difficult, especially at the start of the 2nd and 4th seasons. However, this is necessary both to keep things fresh and to keep the show's overall world and mythology – which is huge, using Baltimore as a stand-in for the American city – working and symmetrical.
Babylon 5, for all its other flaws, also had serialization that worked, in a different fashion. Famously, it was built on a five-year plan, and the creator exercised rigid control over the story – so rigid that he wrote all but one episode over the last three and a half seasons of the show's run.
The premise and overall story for Babylon 5 – the “arc” - was universe-wide, expanding into all aspects of the setting. However, as the series started, the focus was much narrower, on the station itself. The groundwork for the later seasons was built (too) slowly through the 1st season and much of the 2nd, but it was done almost entirely on the station itself. There were hints that the story was bigger, done primarily through foreshadowing, prophecy, dramatic irony, and occasionally ominous whispers about a great evil stirring and the like. As the ambitions of the storytelling increased, it grew to fill in the gaps created by the foreshadowing.
Thus the increased complexity of the Babylon 5 story didn't feel like it was a bunch of added mythology tacked on later once the initial premise was getting tired, but instead built on solid foundations in order to increase the stakes in a satisfying fashion.
This piece is merely meant to be descriptive, not prescriptive. Both Babylon 5 and The Wire required a specific kind of wild ambition from their creators, which is always going to be unlikely to be duplicated. Likewise, just because a show is a mess in terms of continuity and mythology doesn't mean it can't be great. Battlestar Galactica may be structurally weaker than Babylon 5, but I'm not sure I'd actually say that, as a whole, it's worse. And Angel demonstrates that a series can go absolutely apeshit crazy with the serialization and still somehow bring it together.
However, I do think that using the visual metaphors for how mythology springs from serialization is helpful, and how I generally conceive of these things. I hope it helps to explain my point of view on the subject.