cantevensing
you got a couple of things right, and others you got wrong.
the main point you get right:
You'd think male concubines might exist, but this game is geared towards straight men, hence the need for Zeta's apparent patriarchical social relations.
as for the rest, a couple of points of order.
Zetan society is ruled by a few main figures: the queen, who is always called Merneith and always a woman; the head priestess, also a woman. Priestesses as a whole have one of the highest status in Zetan society and are the ones who vet the male candidates for the "vessels" (who, if they make it through the decades of service, will in turn become priestesses). The male candidates are, in this sense, rather disposable and selected for their good physical and character attributes. it is an honour to "incubate" as you put it, one of the vessels... and going at that the other way around isn't exactly a workable path. Furthermore we have a few undefined military leaders and an equally as of yet undefined (mixed genders apply) council of Elders.
The Queen is at the center of a religious cult that is in a way artificial, in that it was purposedly put in place by the founders, but is also rooted in the ancient Egyptian tradition of pharaonic divinity.
The other factions are: Mutants, led by Fangs and the majority of them are women for...reasons... the decayed, who are led by a man, and the raiders, who are divided in several gangs, the one we know of is led by 2 girls.
There are also several Houses of Zeta that are led by women. The one you have already seen in game is the black weapon trader, Mandisa.
Zaton's expectation is that either Shani will leave his house to find her own path and maybe create her own house, or that she will be subservient to him and, in due time, take his place as leader of the House.
Dominance is ultimately determined by personal power, which can be defined by combat prowess, scheming, charisma, personal wealth or any other metric or tool that allows a man or woman to be the winner in the confrontations they decide, or are forced by fate, to enter.
To put it in context, Omar, the MC's brother in law, has a limp handshake but is at the top of his game in the trading world.. he IS a rich and affluent self made man who is the head of his house. If Zaton tried to pull a commercial scheme on him or to get an excessive discount from him, Omar would run rings around him unless Zaton brought the confrontation to his playing field, bullying him with violence. (if he did so, however, eventually Omar would just hire a bunch of thugs big enough to beat even Zaton).
This balance between them, or internal to Omar's House, may remain the same or find a lot of kinky variations in the future, much depending on how those scenes develop, but that is more to entertain the players than to undermine the character, whom we are presented through the eyes and values of Zaton, who definitely sees him as inferior to him, which he is in all the metrics that are of interest to Zaton himself.
There's also, given the highly sexualised nature of the Zetan society, something to be said about D/s relationships from a BDSM standpoint, which again allow for Doms and Dommes indiscriminately...irrespective of their role in their individual houses.
Why do we see very little of that, if anything? Because, as you rightly point out, the game is geared towards a public that is predominantly male and has bought into the power trip fantasy that is presented in the intro, where the main character is the badass leader of his House, there to take names and boink anyone he feels deserves a good boinking.... and a whole bunch of the public gets all frazzled if you introduce them to a hint of another penis on screen, and will start shouting "ntr, ntr, omg ntr, my day is ruined!"
This does not mean that there are no households in Zeta where the balance of power is the opposite. It is even possible that we will visit one or two situations where the MC encounters and interacts with such people. It might even become the subject of a few more sharing, swapping or whatever scenes... that's something for the future...On the whole however, the focus is on House Zaton and its dynamics, and revolves around Zaton being the top dog that he is.
The model of society is fairly recognisable and rings close to our experience or knowledge of a patriarchal society, but that is just the framework, the lore and the content support the roles in that pyramid structure to be held indiscriminately by both sexes.
Male concubines/or sex slaves don't appear on screen because they hold no interest for the main character and the vast majority of the players, not because they don't exist.
In fact, in the scene where you buy Fairy from the merchant (instead of getting her from the decayed brothers) you were initially offered a male slave, sitting in the cage next to Fairy's. That scene was altered and focused on Fairy for simplicity's sake and because, again, male MC, power trip, yada, yada, yada...
Zahra apologises for speaking out of turn because Zaton is the leader of her House.
If a woman other than Zahra had been the leader of the house, and not Zaton, she would have done the same.
Anybody else, from the house or not, male or female, trying to shut her up like that, she would have eaten them alive.
Similarly, when Igor comes to visit, if you have him be serviced by Emilia, he takes his pleasure from her unopposed... if you let Ain blow him, he will try to take a little more than she is willing to give and, despite having been asked to service him by Zaton, little submissive Ain perks up and rebukes Igor and, more importantly, he apologises to her, not to Zaton.
If women were flat out subservient and not meant to have their own agency, this would not happen.
What marks the difference between Emilia's scene and Ain, is the status of the 2 women in society and in the House they find themselves in.. consequently, their freedom of self determination.
There is a possibility that we will see more varied familiar compositions in side characters actually take part in scenes or be at least represented on screen more fully, but that is for the future.
As for the disregard of consent... that is again not so much a product of patriarchy as of the victor of a confrontation having right to the spoils of war and this being a generally accepted result, universally understood by all parties. In that sense, we ride a subtle line as far as consent goes, and I agree it's mostly semantics, but it works, and the lore tries to support it.