Realistically, we know that no-one’s level of happiness here in the present is determined by standards of living in Manchuria in 1941. You can argue the point intellectually that we are all very well off compared to most humans who have ever lived. Nonetheless, psychologically speaking, people’s satisfaction in life is determined by more local comparisons. (If new historical research showed that Manchurians in the 1940s were actually having a whale of a time, would that make you correspondingly miserable? Of course not!)