"the first book-length work of ethnography I’ve read"

Somewhat uncharitably, I'd suggest that you still have the first work of ethnography to read. I think the key feature of any ethnography since about 1920 is the search for meaning rather than superficial features of the observed. It's not what sense the observation (no matter how accurate) makes to you, it's about what sense it makes to those described.

The question of whether you can generalise these observations is really the wrong one to ask in this sense. The things Semyonova describes are commonly found across cultures but they do not necessarily  'mean what you think they mean'. You should really be asking, can I particularize my assumptions about what the 'good life' is?

An example of this is conflating rituals with their surface meanings. For instance, the examples of brides wailing at their wedding or mothers insulting their children are not particularly disturbing if you think of them as conventionalised expressions. Many cultures will be hesitant to compliment children lest they attract attention of evil spirits. The idea of children being constantly told that they are being loved or they will be forever scarred is a recent American invention. Sure, the children's lives were pretty miserable because of the poverty and disease but gruesome lullabies are not an evidence of this. Neither were 9-year olds taking care of younger siblings. Semyonova didn't have the advantage of reading other ethnographic accounts, so her observations were colored by assumptions about normative families. I recommend David Lancy's "The Anthropology of Childhood: Cherubs, Chattel, Changelings" - the subtitle says it all. 

Also, it is dangerous to equate ritual humiliations to real ones. Many cultures will sanction vicious practical jokes while at the same time placing great value on individual dignity. They just differ on what constitutes such dignity. The conditions of brides in patrilinear societies were often ritually very degrading but the actual conditions were more complicated. The women were not be brides forever.

The question of gender is always a complicated one. You will notice that women were as much perpetrators as victims of the oppression of women. While domestic violence would have been rampant, it is hard to know the extent of it compared to other cultures just based on Semyonova's account. It would probably not have been that unusual even in the cities of her time.

Of course, Semyonova had a point. The Russian peasant or the Kalahari bushman (of Sahlin's 'original affluent society') are not some noble primaeval exemplars unspoilt by modernity's alienation from what it means to be a true human being. If you want many more much worse examples, go to Robert Edgerton's 'Sick Societies'. (Pinker mentions some of those.) But even Edgerton cannot help but acknowledge that individuals can and do find personal happiness and fulfilment even in these contexts.

In the case of Russian peasant women in particular, their “connection” to husbands who beat them, in-laws who scorned and humiliated them, and a community that offered no support, was not enriching but immiserating. 

This is where Semyonova fails you the most. Those people were connected in myriad of ways which made any survival at all possible. She essentially treated everyone as little middle class nuclear family units - but the peasants would have been a part of much wider kinship networks which is what would have ensured survival. A modern ethnographer would have started with outlining kinship networks and their interconnectedness. At least from your account, she did not do that. 

The peasants would have also been involved in a lot of religious observance with a political dimension. I can't find the reference, but there was a lot of turmoil even in the 1700s to do with religious reform and the politics of baptism. These were not just stereotypical wife-beating drunks, who ate gruel and kicked their children when they annoyed them. 

It is also important to note that East European peasantry of that time were less than 2 generations away from the abolishment of serfdom - so essentially dealing with the legacy of conditions that were only marginally different from that of slavery. Those conditions would have also imposed limits on social structure and organisation that were to persist until collectivisation and mechanisation - when they came to be seen as 'the good old ways'.

The escape from those “connections,” provided by wealth, education, and opportunities for jobs and migration, would have been a boon.

This is a very ahistorical statement. To escape to the opportunities provided by wealth in the last 40 or so years, perhaps, when it is backed by socialist state capacity (and America is socialist in this sense). But to escape to the cities of their time, particularly women, would have been much more exposed to exploitation and most would have found it very psychologically stressful. Accounts of the urban poor are, after all, not any more difficult to find or less harrowing to read.

There are no easy conclusions here. It's hard to imagine living in those conditions and find any sense of thriving or wellbeing. But people did. Not all, not all the time. There was no inherent virtue nor nobility in those conditions, but there was humanity - in all that it involves. I think any notion of progress needs to start with the acknowledgement of that complexity. 

Opponents of progress make the opposite mistake because they see themselves as defending some imaginary romanticised essence of humanity. But progress studies, should take contextual meaning more seriously. Because without meaning, what are we?

Thanks for these questions. I think Restall's and Thorton's books will answer these adequately. But Sharman's 'Empires of the weak' is even more forceful in this thesis.

However, Scott's 'Against the grain' is also an important element. Essentially he argues against the conflation of the civilisations with buildings and recorded institutions with 'nations' in today's sense. Most people were not controlled by them until much later. So while the 'silver mines' were indeed hell on Earth, they represented a sliver of the population. Cortes and Pizarro managed to destroy relatively new and hugely unpopular empires by relying on local allies (and they were learning from each other in that). They achieved nothing like the control the Nazis did in Poland or France. They were much less successful with the Mayas who were already more fragmented and therefore more resilient.

The Portuguese in India did the same but managed to just snag some edge disputed territory and became just one (very minor) of the many players in the region. Remember they achieved nothing of note in Japan and even less in China (until 300 years later). Yes, they got some port cities on the coast of East Africa but they very tenuous holdings. It is important to look at not just where they succeeded but also where they failed. If you're looking for some successes, I think the Spice Islands are more in that vein but even there things did not always go all the well.

The reason why all these Europeans did this at the same time was as you describe: they were learning from each other and were exporting their competition abroad. Opportunities for growth in Europe were limited, the Ottomans were making trade with India more difficult; and the religious aspect was also important - Columbus was not just after trade but also opening up a westward route to Jerusalem (and finding the mythical Prester John). The people in the places they came to were not interested in exploration. The Aztecs had loads of space to look out to (and just try to hold on to what they had), India had lots of trade routes going in the other direction. China was building walls against the steppes and thinking it was already the center of the Universe. Etc.

When we think of Cortes and others as 'conquerors' we're essentially just buying into their propaganda. Which is partly why I used the word tendentious in the first reply.

Perhaps, I should have phrased that differently. In the 1800s, the historiography was not so much tendentious as unreflective. The books I list certainly have a point of view. But they are aware of that point of view and do not hide under "primarily trying to recount events". Because any recounting involves selection and emphasis and selection is always personal (ie epistemology is ethics). The books I list point out the gaps in those accounts and offer a way in which we could think of the past with those gaps filled in (and perhaps choosing other things for the gaps).

For example, when you say something like "Europeans conquered the Americas and India", this only makes sense if you stick with the Cortez et al. winning battles and controlling territory narrative. These things happened. But actually the answer to "How come these people conquered X" is, "They didn't". You are viewing it from a nation state WWII perspective (Germany taking over Poland, France, etc) and from the point of view of the eventual outcome 500 years later. The other narrative that intrudes is that of the 1800s 'British Raj', 'Opium Wars, and 'Scramble for Africa', 'American Westward expansion'. But in 1800, nobody was expecting the world to look like it did in 1890. China and India were still major powers (India not as a unitary state), most of America was not under control of anything like a single power, Indians were winning as many encounters as they were losing, Europeans in Africa were helpless and mostly supplicants to local powers, Ottoman Empire while on the wane was still a major player, Japan was still closed to the world, etc. The year 1800 saw no steamships, no trains, and much of what we think of as industrial revolution was in textiles manufacturing and mining. Europe was in the grips of major conflicts and losing as many colonies as it was gaining. If you look back at the time of Cortez from 1890, it will look different than if you look at it from 1800, 1700, or 1600.

What this revisionist historiography does, is look at that time with those lenses, as well. (And because it is the current trend - sometimes taken to extremes - it is will seem as tendentious.)

To add, if you really want a very comprehensive look at Cortez, read Restall's most recent book 'When Montezuma met Cortez'.