But in a serialized setting each episode is a chapter in a larger story being told. And if they are an exercise in wheel-spinning then yeah, they aren't serving their purpose. IMO, a major purpose of a chapter in a novel is to be additive, not neutral and not subtractive.
But why does a show have to be
purely serialized or
purely episodic? That kind of binary thinking is the problem. Many, many shows have done well with a mix of the two, like
Deep Space Nine or
Babylon 5. I think it's good to have that mix of approaches. It gives a show versatility and variety that keeps it interesting. A good piece of music doesn't have a single constant tempo throughout -- it varies, has different tones and different paces, to create contrast and counterpoint. A good story does the same. Even when you have an overall arc, it's good to step back from it sometimes, let it breathe. After a big event, it can be good to slow down and deal with a side story so the audience and the characters have time to process the really big thing.
And let's talk about novels. I've written a bunch of them. And I've often found it useful to insert "episodic" chapters, to pick up with characters after a transition in their lives and take a little time to establish their new status quo with a relatively standalone incident before moving on into the main arc. I did it in
The Buried Age, I did it in
Only Superhuman, and so on. Novels need varying pace and structure too. Everything is a piece of the whole, including the self-contained parts. Just because something isn't obviously, directly advancing the main arc does
not mean that it isn't additive to the story, because the arc is not the whole work, just a component of a larger whole. A figure needs a ground. Music needs rests as well as notes. Art relies on contrast, and on context.
After all, the writing staff of a modern TV season breaks the entire season's structure as a group. It's not like they plot out an arc, then stop and say "Whoops, we came out one episode short, let's find some unconnected story we can randomly stick in there." No. Of course not -- at least, not unless the network decides to extend the season order or something, like FOX did with
Lucifer a couple of years back. But normally, if they choose to put a standalone tale at a specific point in a season, that's because they decide it belongs there at that point, because it serves the overall whole to have that piece there and not somewhere else. It's because they have a
reason to tell that story at that point in the characters' lives. So it's naive to dismiss it as unimportant.
(Although a couple of the standalone episodes that
Lucifer's producers made rather than padding out the planned story arc proved to be some of their most striking and impressive installments, and proved that episodic storytelling is something we don't get nearly enough of anymore. Episodes that are just chapters of serials are rarely memorable in themselves, but a good one-and-done can stand out in your memory for the rest of your life.)