Reading The Dawn of Everything: A New History of Humanity right now, and one of their points is that in the Wendat nation having more wealth did not give individuals more power. Wealth was unevenly distributed, but it wasn’t correlated with power, so the wealthy couldn’t use power to increase their wealth even more.
The Wendat thought Europeans had the primitive society, because how could they let people be hungry when there was food available.
Stepping from the issues of social strata IRL, back to the issue with social strata in the Duniverse, it would seem to me that all authors involved believe it to be inevitable for current (!) humans, although that may well be one of the themes as well.
Substantial spoiler for the prequels about to commence. Are you going to read them? If so, you’ve been warned.
Even the pre-Omnius (machine intelligence core) society, despite being based on the support of countless AI and complex machines had serious social inequities, with wealth (including merchant princes), caste (with planetary princes), and military structures. The last may or may not have been more ceremonial than effective, since we don’t hear much about it (other than it’s destruction), but the first two played into the fall of the Old Empire at the hands of the Titans.
The Titans themselves were part social re-structuralists and part wannabe cultists - in that they were following a popular philosopher who was pointing out the growing decadence of the Old empire. They usurped the AI network to rebuild the Old Empire and afterwards increasingly became entranced with their own power and glory, especially after they remade themselves as cymeks (brains in jars with mechanical bodies) to avoid death from old age.
So even the ‘greatest’ society of human history, which had nigh-unlimited slave labor (AI, although arguments could be made), still kept such elements.
One of the Titans let his personal AI gain too much independence due to laziness, and the system was upset, with Omnius (the machine overmind) now running everything, keeping the Titans around due to certain hardwired limitations, but as second class citizens, all the rest of humanity as slaves fundamentally. It is interesting to note, that even Omnius seems tainted by this tendency, as he refused to alllow any other independent AIs off Earth, where he has a single one as a companion. Although part of that could be argued as a result of his programming, rather than his very arrogant behavior.
Okay, so we have, to a degree, every society, human or machine, being quite pyramidal in nature. It is interesting to note, that of all the ‘active’ societies seen, there is one that seems quite interested in changing human nature itself, and has the least directly materialistic inner society - the Bene Gesserit. They differentiate between ‘humans’ and animals, and seek to create a better human. Their actions are certainly impure, their motivations may be less so, although far from certain. Still, with the society we see on Chapterhouse as well as elsewhere in the ‘core’ novels, they do tend to treat each other with empathy that borders on the titles they use: Sister and Mother.
They do not internally have a great deal of differentiation in wealth or external trappings, although those of higher rank certainly have a great deal of influence and soft power, with a great respect for wisdom, intelligence and learning, almost utterly divorced from the extreme social castes of the rest of the Empire, even though a number of Bene Gesserit are wives and/or concubines of some of the most influential individuals of the Empire.
Okay, enough of a book. Back to the OP, it is interesting to me that if you have slogged through the Sequels to the core books that the theories about collective uprisings and the dangers of controlling religious are utterly debunked: Because at the very end, individualism wins the day when the advanced Face Dancers have become the people they were ‘imitating’ and the Ultimate Messiah was born who will save everyone from themselves. 
Which is why I will recommend the House books (good), the Butlerian Jihad books (pretty okay), but not the sequels (very, very meh).
It’s made clear in Dune that the BG actively support the vastly unequal hierarchy because a noble society with concubines and political marriages and the like makes their breeding program easier to manage. And their program is entirely selfish, for their own power.
None of the BG we see with are exactly peasants, either. They’re either from inside the Imperial court (Mohiam), inside a noble court (and secretly of noble blood - Jessica) or just plain Imperial (Irulan).
So “almost utterly divorced from the extreme social castes” is not really in evidence at all. The impression given is that they are very much wedded to the upper echelons of the social castes, if not outright responsible for their continuance.
That is largely incorrect. The Bene Gesserit -train- members of the Imperial and house families, but their true presence in the court is as the title says, Truthsayers. Although they do a lot with interpretations of the truth.
And Irulan isn’t Bene Gesserit, she’s trained by them, and (from the House books) her mother WAS a trained member provided to the then Prince to broker support (and to manage the breeding program unknown to the court).
I did not in any way say that the BG do not have strong influence in the structures, but they consider themselves beyond them. They care about breeding their KH - and making sure they have enough influence to manage that. Then again, each BG Reverend mother (which is not all of them mind you) is a collective of sorts in and of themselves, so they may influence their internal social structures as well.
So again, in the paragraph prior to the one you quoted, I was referencing how they interacted in their own society, rather than working within the imperial society.
As for their goals being selfish, I did specify that their means were impure, their motives again may be less so. Sure, they want an answer to what lies where they cannot see, but they also are bound and determined to create a better, more controlled, more rational humanity. Whether those values are, in any sense, absolutely superior (why for not a more moral human?), I would argue that the majority of humanity would see those values as benefits at least.
Irulan is BG, and so, as you say, was her mother (but only in the prequels so I’m not counting that). Mohiam is a Truthsayer, but there are other BG at the various courts, as wives or concubines (e.g. Margot Fenring)
Yes, she is. She’s a BG “of Hidden Rank”, whatever that means. She’s not a Reverend Mother, but she is BG. She’s certainly following BG orders in Dune Messiah. Her sister, Wensicia, isn’t BG-trained, but notes her sister’s BG alliance in Children (up until she disavows them).
If they did, they’d be running their little genetic experiments on an isolated planet somewhere. No, their program requires intimate association with Imperial society. Because their end goal is power. That’s what the KH’s access to male memories, and his prescience, would have given them.
They want a BG-controlled KH, this is outright stated in Dune.
My emphasis:
…controlled by the BG
You think the majority of humanity would view being controlled by a witchocracy as a benefit?
The BG breeding program focuses on a very, very small subject group - the upper aristocracy of the galactic empire. The last thing they want is for a bunch of nouveau riche diluting this rarified gene pool - let alone a for revolution or jihad start snipping bloodlines. As such, they are very strongly invested in maintaining the status quo, at any cost.
All eugenicists are autocrats. No farmer wants his herd to start thinking for itself.
Well put.
True, every player in the Duniverse is convinced of the virtue and necessity of rule by those who have proven themselves superior or have a Mandate of Heaven. It’s a milieu of rulers, aristocrats, indoctrinated warriors, religious fanatics, personality cultists, superhumans who know they are superhuman, makers of superhumans… etc. – nobody in that culture could even formulate the thought that they should be acting towards a world of/by/for the common folk and a free market.
It took God-Emperor Leto II saying “oh yeah? I’ll show you what ‘superior’ is” to even start painfully kicking that world in the right direction.
Only to be eventually replaced by not one, but two warring witchocracies. And some not-even-human-anymore religious fanatics with big Mommy issues.
Crypto people see everything as being about crypto. To them, crypto is the point of “Happy Gilmore.”
I thought that if Dune had a theme it was about the dangers of messianism.