On the same line, you seem to have a superior knowledge as to the breadth of my education than I do myself. As this is a matter of some concern to me, perhaps you could offer some helpful suggestions on how I might improve my self-knowledge?
This line of thought wasn't really even on my mind in replying to you, nor for that matter was I originally thinking of debunking Marx or getting into a political debate (much less this one). However, now that you mention it, your sources do seem fairly transparent to me.
Without having read the Britannica article quoted, it's a little difficult to see why that Encyclopedia declared matriarchy hypothetical, or the basis on which it deems this a consensus view.
It's deemed the consensus view because there is absolutely no evidence for the existence of prehistorical matriarchy at all. There is more evidence for the existance of Atlantis and UFOs than of the prehistorical matriarchy. I don't see how its difficult to consider it hypothetical, and even hypothetical is giving it more credibility than it deserves. Even the evidence of some sort of formal power sharing strikes me as rather weak, given that ancient Greece was among the most chauvanistic societies that ever exist despite featuring feminity prominently in its conception of the sacred, yet its the pre-historical Greek society that is held up as evidence of the theory.
And as far as the whole patriarchy arose out of a slave holding society thing, that's directly out of Marx's writings on Historical Materialism. You are describing the standard model of stage two development in society according to Marx, with a bit of second wave feminist critical theory thrown in. I don't have enough time to shoot all the holes in that that can be shot, nor is this the place to do so, but I think its sufficient only to raise the issue of livestock as evidence that patriarchy would not have to be based on slave holding. And an even bigger hole can be blown through the whole fantasy construct by pointing out that gorilla's and chimpanzees manage to maintain a social structure centered around dominate males without having a concept of private property more complex than 'this food I'm holding at the moment' which suggests no transition stage may have ever existed and certainly none ever need exist. Brutality and the will to use it would seem to be sufficient to me, distasteful of a concept as that may be.
Wikipedia's further discussion on late 20th C. and 21st C. anthropology seems to indicate that it's been defined out of existence: there are matrifocal, matrilinear, matrilocal, anything but matriarchal societies.
Well, except that it got defined out of existence not by the detractors of the idea, but by the supporters - defensively as it were - in order to keep having something to write about and justify their careers with.
Look, I'm not at all saying that historical patriarchies are not unjust and frankly the whole ideal I find rather repulsive, but the universality of patriarchial societies in the pre-modern world is well documented.
But if you buy that, then the same move can be applied to patriarchy. There are societies which are focused on men, in which descent is primarily measured by paternity, etc, but none which are ruled by men simply because they're men.
In almost every government of medieval Europe, a eldest daughter would not inherit the throne, title or property, if a younger son existed he ruled
simply because he was a man. In modern Saudi Arabia, if you are a woman and your younger brother orders you not to do something, and you disobey, he has legal right to discpline you
because he legally rules over you simply because he is a man. I think that's fairly sufficient to prove that patriarchial societies existed and often still exist, even if we didn't keep reading down the wikipedia article were it talked about prohibitions against female rule in Islam, Judism, Buddism, and Hinduism (which I would think would cover a fairly large slice of humanity).
While I know that it's common to regard Marx as putting forward statements of that type "Y happens regardless", such a position is scarcely credible.
There are a lot of things that Marx said that are are scarcely credible, but that doesn't mean he didn't say them. If Marx can be easily shown to be internally incoherent, that does not detract from my point in any way.
Look, if you want to talk about creating worlds that feel believably non-modern, believably feudal, or simply believably alien then I'm all for that. If you want to have an argument over Frankfurt school critical theory, I can't really do that here. My thought at the time didn't include Marx or feminism at all, and if you must know what was going on in my mind, it was more anti-Jared Diamond. I was suggesting that world building ought to be more about building a geography; it must also be building a history. Someone was asking me how these different social models managed to arise, and I was answering in effect, "Because people chose them." If you think that's a trivial and superficial answer, then there is little I can do about that.
The government owns everything by right of conquest (by William the Conqueror). The tax system assumes that the government owns all our income, but may deign to let us have some of it back. It does mean most of us don't have to do tax returns though, which is handy. 
