Well, there are the billions who are now alive thanks to modern agriculture and medicine. We are perhaps comparing the best of the past with the worst of the present, which may not be a fair comparison. Best is to collect the best of past and present to create the best future.
But it also matters how those billions live, and considering that the vast majority live in extreme poverty the picture becomes less rosy. Not to speak of the ecological disasters of climate change and pollution this is causing, which also has an impact on our well being. Modern agriculture and medicine have in a way made it possible for all those people to be alive at the same time. I agree with your last sentence since we obviously can't change the past.
For that matter, the whole point of the primitivist argument is that humans have been quite happy about living in extreme physical deprivation for most of their history. It's only when the social milieu is totally FUBAR that "poverty" as we know it becomes a cause of deep unhappiness and dysfunction. Also as the OP shows, people can also be quite unhappy with their life despite living in a highly developed country and enjoying quite a bit of material wealth.
