I think I've mentioned it on others of your threads, that I understand a lot of what you're going through, having either been there myself, or because I undertake a lot of the same work, with the complexity of my world and the variety of characters within it considered to be "central". So, I don't think that to balance complexity you need to simplify, necessarily. Rather it's a matter of sifting through that complexity and refining your focus.
As a "for instance", I've put eleven years of work* into my world, the characters, and the stories, and every aspect therein has mutated throughout the process. I started with the belief that I wanted to tell the story of a few characters, those that I'd developed near the beginning, and I still do. Then I had the desire to tell of their** journeys from being disparate individuals scattered across the world to fully awakened beings of power, and I still do. But what every one of these stories has in common, more than anything else, is that they orbit a central story arch that has been in place for the last eight years, at least. They hint at it, they reveal things about it in increments, they illustrate how the world works and how these people came to be what they are seen as, and ultimately sketch out their placement in the main plot. In the end, though, they don't directly contribute to the telling of the central arch. What is necessary from them, as characters, is their presence as fully awakened beings of power, and their participation together. How they got there is much less important.
That was my realization, my refining of focus, because knowing a thing is the crux of all your hard work, and allowing the pieces that don't directly contribute to remain on the periphery, not forgotten, but not demanding more of your regard than they should, are two different cows.
I think of the complexity as being the difference between making up a setting for a story about two people meeting for lunch, and telling a story about the day you and your best friend of twenty years went out to lunch in the town in which you grew up. In the former, you could be making things up as you go, sketching out only the areas in which the reader sees the characters, whereas the latter lends depth naturally, because you know the town like the back of your hand without even having to think about it. That comes across to the readers. You lace the story with information as needed, for color, for context, without drowning them with details you think are amazing, because you just came up with them and want the reader to know about it. That's how I regard world building and its purpose. We build for ourselves, for the characters, for our own knowledge. We don't have to choke the reader with the brilliance of that work (as, obviously, it's all brilliant). It's there so that when we need something we don't have to grope in the dark until we find a Something that works, because the Something that already fits perfectly is quietly existing, firmly ensconced in its perfect place.
What is it about your world and characters that draws the other pieces in? Is there a thread that binds them? Is there something around which they all seem to revolve? A theme? An event? An individual? What story do you think you're trying to tell, and is that really the story that wants/needs to be told? Sift, play, build, experience, plot, renovate, kill, destroy, resurrect, deify, curse, jumble, chase down plot bunnies and orphaned thoughts, generally wreak havoc with your darlings. Somewhere in there is what needs to be told, and of all the pieces needs to be exposed to the most light to thrive, and its triumph doesn't need to eliminate the others in order to get there.
* Off and on, mind.
** No small task, considering what had been three had become fourteen in the intervening years.
