So, consider Death of a Salesman. In the grand scheme of things, Willy Loman is not important. Indeed, that's his definitional characteristic. That he is unimportant is in his name, "Low-man". His unimportance, and his struggle with it, is what the play is about. In the end, Willy thinks the payout on his life insurance is more valuable than himself.
I've taught
Death of a Salesman. A character doesn't have to be important "in the grand scheme of things" to be important in the story. In fact, Loman's unimportance in the grand scheme of things is the entire point of the play.
What matters is his importance to the story. Specifically, to giving it stakes and meaning. Considering that it is a canonical text, and he is a canonical character, I would say Miller was fairly successful in building a compelling story around Willie Loman's unimportance. Or, put another way, Loman is
central to the grand scheme of things that matter in the audience's universe: the currently unfolding story.
His story, one of the classics of American theater, doesn't matter? The fates of ordinary people who don't have major impact on the world, don't matter?
You are totally missing what I am saying about the deaths of the characters in
Agatha All Along. The ones who die essentially get fridged, and for what? They are there to die, to try to give the story stakes, but the story goes nowhere. I could care less about their importance in this fictional world, my point is that they are unimportant in this story, because the story essentially goes nowhere. It's all set-up.
Hey it turns out the coven member who survived had been originally cursed by Agatha - whoops! Which was dealt with in a couple of minutes and see ya. There's a meaningful character arc.
Yeah. Tell Lilia that. Oops, you can't, cuz she died. She sacrificed herself for others. No stakes at all for her, though!
No stakes for the audience, which is what matters. It's not like Lilia is a real person, and it's not like her death actually meant anything in the story. I mean, had the series ended after episode 8 you could have argued that she was there to teach Agatha about sacrifice. But in the end, Agatha sacrifices nothing - she just powers up.
The entire series existed to introduce a new Avenger (maybe; see Kang above) and make Agatha more like her comic book self. Mission accomplished, I guess, but it does so at the cost of giving the series any independent reason for being. Specifically, its own story. The whole series is just backstory. Which is true of almost all D+ MCU shows.