Earlier quoted context omitted.
You can make a lot of ideas make logical sense if you create the correct framing, which you did in your post. However, your frame excludes the discrepancy between single males, who could vote, and single females, who could not vote; we can recurse, and say that single females could barely exist in the middle-class world due to social and economic norms which prevented women from getting jobs above starvation wages, a…
But his point still stands.. the lens of chronological snobbery is intellectually dishonest regardless of “framing”. Our modern society is radically oriented towards the individual, and not the family. That does bias our view of how good or bad a previously family-oriented society was. It’s hard to fully quantify the long-term implications of that change.
There is no reason to think that a single marriage is the best format, other than it happens to work well within the framework we've built up to support it over the last few hundred or few thousand years in specific countries. So the individual is it, because it's common to all.