This is a great question, but I'm afraid the answer is that, no matter what you read, we don't know. Not with much confidence, anyway.
There are some broad strokes we're pretty sure about. But there's lots of details that we have to speculate and infer. We can't really extrapolate from modern hunter gatherers because they are atypical in that they are the only hunter gatherers that stayed hunter gatherers after the widespread adoption of agriculture. Same for extant pastoralists (who didn't convert to ranching).
We face similar problems trying to infer what early humans were like from achaeology and from animal studies. We can make some educated guesses, but the degree of accuracy is low.
I think it's reasonable to say we know insufficiently much about early humans to help you answer the original debate you were having with sufficient confidence to conclude much from it.
What frontier archeology research is necessary to resolve the question of, e.g., ancestral human reproductive community size, then? I know we're confused as a civilization. If you don't think it's because there's some great theorist we haven't caught up with, then what evidence remains uncollected?
I think the evidence simply doesn't exist and can't be collected. We might get lucky and find something definitive, but more likely we'll keep finding tiny clues that can be interpreted multiple ways with low confidence.
This is akin to the problems we face in paleontology. It just doesn't take very long to lose so much inforamtion that we're left guessing based on crumbs.
I think ancient DNA analysis is the space to watch here. We've all heard about Neanderthal intermixing by now, but it's only recently become possible to determine e.g. that two skeletons found in the same grave were 2nd cousins on their father's side, or whatever. It seems like this can tell us a lot about social behavior that would otherwise be obscure.
I recently got into a chatroom debate with some very smart people about whether homosexual behavior was typical for humans [ not bonobos ] in the ancestral environment / Environment of Evolutionary Adaptedness [EEA] [ i.e., ancestral hunter-gatherer society ] -- and, connectedly, how big was the social circle that the median ancestral human probably had occasional contact with [ not "Dunbar's number", but "how big is your meta-tribe ].
I felt like I knew what I was talking about . . . but not nearly as much as I would like to. For example, someone linked this study, which claims the egalitarian hunter-gatherer model is missing important pieces and stratified societies existed prior to agriculture. I doubt this, but I feel like the basis on which I doubt it is shakier than it needs to be.
Then I found this article, which says:
Whereas the chimpanzee community is only partially a closed reproductive unit (Wrangham 2000), the larger size of hunter-gatherer communities (typically 250-500 in contrast to 40-150 among chimpanzees) renders it a more adaptive breeding isolate (cf. Wobst 1974) and intracommunity marriages play a crucial role in cementing relationships between bands.
This seems plausible, and would affect my framework for thinking about psychology greatly, but I'd never read about it before [specifically the "dating-pool communities tended to be 250-500 members big" part]! Who are the brilliant theorist-writers that I need to be looking to, to get caught up on the details of how human ancestral society worked?
Texts I've found useful for getting a picture of ancestral human society [ they all involve studies of living peoples and I suspect this is a load-bearing component ]: The Dobe Ju/'Hoansi by Richard B. Lee, Growing Up Yanomamö by Michael Dawson, and Primate Sexuality, ed. Alan Dixson.