Not going to lie, this is a bit of a slog to read through. You've done a LOT of work to set the scene. The details seem to encompass the breadth of Frank Herbert's 'Dune' for an introduction! I do wonder, though, if the format could have been revised a little so as to clarify a bit more of a lean central narrative with the extended information available in bite-sized pieces?
Lore question: You mention people would be willing to do slavery rather than resort to cannibalism... and I wonder why this would apply to every culture? Could it be that in a hypothetical world subjected to extreme calamity, cannibalism is considered a sacred alternative as compared to subjugating another human being? I kinda wished that one's actions resulted in things happening -- such as the brood being more active in an area because they (evil ones) can recognise stirrings of evil in a human settlement? ie. additional abstract rules to account for how the players play.
Perhaps the lore in this source book is but one perspective of what's actually going on in the game world? And thus creating other compatible texts based on the same world (but from other perspectives)?