> We know a lot about the lifestyles of european benedictine monks, for instance, because they were excellent record keepers, but we still can't answer basic questions about their lives.
That's why finding their garbage or where they emptied their latrines is often more insightful than finding yet another written record.
Only because they have left so much written record that we don't really expect that another record will tell us something we didn't already know. The less we know about some culture the more valuable written record would be - but often it isn't available. When we already know a culture well archeology can tell us where they ideals they wrote about themselves don't match reality. When we know nothing though, archeology leaves us with a lot of evidence that we don't really know what to make of.
Maybe. Though people rarely write down the things that we now find most interesting.
Have a look at very old newspapers or magazines. It's almost irrelevant today who won the latest elections or what scandal happened to whom; the old ads are typically the most fascinating part.
Similarly, we have a treasure trove of old clay tablets with complaints, mundane contracts, letters by normal people etc. See https://en.wikipedia.org/wiki/Complaint_tablet_to_Ea-n%C4%81...
Those are much better at shining a light on how people lived, then the typical drivel about 'important' events we get in most early writing.
Anyway, with this specific article social stratification is one of those things with little ability to extract a narrative from a single data point, but whose importance emerges when collated with others. And it does sound a bit editorialized for modern narratives, but that's probably not intended by the researchers.