I feel like you're missing something... Runeterra is wide.
There are big players, and there are smaller players. Whether it's regions or characters, there are some who are really important in Runeterra's history, and some who are not. It doesn't mean they shouldn't have stories.
The stories you've cited are part of the larger scope. They involve very important stuff in Runeterra such as Darkins, the Watchers, and the Void. However, these aren't the only existing stuff on Runeterra. There are less important stuff on the larger scope of things, but it doesn't mean they shouldn't be treated.
Stories like The Echoes Left Behind or even Silence for the Damned don't involve the Void or the Darkins, but it doesn't mean they aren't interesting. They might not interest you because they don't evolve world-ending threats, but that's all.
Actually, I'm glad Riot doesn't just focus on the Void or the world-ending threats.
I'm gonna give you my own example-
As you may know, I'm a Syndra main. I love my champion, and the different possibilities of her lore. Syndra is not a big fish in Runeterra. If you ask me, she has the potential to be, but some people think she won't ever be significant. Does that mean she shouldn't get lore, because she's not "big"? Not "important"? And I say Syndra, but she's not the worst offender because given her background, she has the potential to be big, but what about champions like Talon (hi, Lewanor!)? I mean he's a normal human, he's not "important" (according to what I think are your criteria), so he shouldn't have lore?
My point being, just because a story doesn't involve the Void, or the Darkin, or the Ascended doesn't mean it's bad. There are 140+ champions. All champions will never have the same amount of lore because some are more important than others (I often use Lissandra and Syndra as an example. I know Syndra, despite all the potential I see in her, will never have as much lore as Lissandra because Lissandra is much more important for Runeterra), but it doesn't mean they should be avoided. Riot has invested in their Worldbuilding a lot. If they just wanted to tell one storyline (that of the Void, since all stories you mentioned are results of the Void's invasion), they wouldn't have.
Now don't get me wrong, I understand your desire of wanting more "worldwide" lore (if that makes sense?), but I disagree with the fact that the stories have been uninteresting so far. It would be disappointing if they were to ditch every "less important" champions in favor of always the same champions that are tied to the "bigger scope". Like, we got Lissandra's update not so long ago (less than a year), and there's already a teaser for her (which may or may not be about lore. Also I'm not targetting Lissandra in particular but since she's example I have rn...). I'd gladly accept any kind of lore they throw at us involving Lissandra. But imagine if there were Lissandra updates every 5 months or so, and never for the others (I'm not saying it'll happen, but just imagine)... Some people would be happy, but what about the others? What about the ones whose champs are "forgotten"? I for one, would start being really upset.
Runeterra is a world like ours, deep down. There are big things happening, and there are smaller things happening. It doesn't mean the smaller things shouldn't be told and are uninteresting.
Of course I am biased, because my favorite champion, Syndra, currently exists in a vacuum, and isn't "important" - and it's up to Riot to decide if she'll ever be. So obviously, if she was forgotten for another "bigger", important champion, I would be really, really mad. But overall, I don't think it's fair to say it's uninteresting because they try to cover as much places and champions as they can.
