I don't know how all of the factors you bring up interact, but as far as the last point: the universe is indeed uniform and isotropic at a large enough scale (~300 million ly), called, nicely enough, the End of Greatness ( https://en.wikipedia.org/wiki/Observable_universe#End_of_Gre... ).
Its confusing to me that this would be the case, when the Bootes Void alone is ~330M ly in diameter; and that's small. The Canes Venatici Supervoid is upward of 1300M ly in diameter; the LOWZ North 13788 void is potentially as large as 3000M ly; the list goes on. We've detected over 100 of these supervoids larger than the "End of Greatness"; and that's just what we've seen so far.
Obviously, supervoids are a part of universal uniformity, at a large enough scale, but I'm having a hard time rectifying that the scale we're talking about is ~300M ly, and not significantly larger, with the fact that there are, trivially, a large number of "300M ly windows" one could pick, anywhere in the universe, and see extremely different things. In some cases, an extreme density of billions of galaxies, and in others a number that is dwarfed by even the number of large bodies in our own solar system. Is this a situation where we just didn't know about these 300M+ ly superstructures when that scale was calculated, and it needs to be revised? Or we knew about them, the math would naturally allow for a level of deviation, and to this day they're still rare and small enough that the deviation is low? Or is there something about the math I'm missing whereby discovering any number of these, into the future, still allows that ~300Mly number to work?
> In some cases, an extreme density of billions of galaxies
I think you might be overestimating how dense a galaxy is, in the grand scheme of things. You may think it's a long way down the road to the chemist's, but it's still almost entirely empty space.
Obviously, supervoids are a part of universal uniformity, at a large enough scale, but I'm having a hard time rectifying that the scale we're talking about is ~300M ly, and not significantly larger, with the fact that there are, trivially, a large number of "300M ly windows" one could pick, anywhere in the universe, and see extremely different things. In some cases, an extreme density of billions of galaxies, and in others a number that is dwarfed by even the number of large bodies in our own solar system. Is this a situation where we just didn't know about these 300M+ ly superstructures when that scale was calculated, and it needs to be revised? Or we knew about them, the math would naturally allow for a level of deviation, and to this day they're still rare and small enough that the deviation is low? Or is there something about the math I'm missing whereby discovering any number of these, into the future, still allows that ~300Mly number to work?
More to read, I do believe.