I don’t think that’s OP’s point (plus I’m not convinced we really are more productive). OP’s point appears to me to be something like “a good measure of productivity is how many people a single working person can support”. Today, most families need to have two parents working. This makes a pretty good inference, I think, about how much things have changed.
Most families do not need to have two parents working if they live like people 60 years ago. Ie one car, a 1000 sq ft home, vacations in the local area, home made lunches, hand me down clothes, no AC, no electronics, no braces.
Good luck convincing people that they should be happy to raise children with the living standard of 60 years ago and they don't have to worry about money because there's free activities to do with your children.
What you call "chasing the joneses" is perfectly expected human behavior. People compare themselves to their current metaphorical neighborhood in time and space (not to their grandparents or to hunter-gatherers) and they make their life decisions based on that: college, career, having children. It's just nonsense to dismiss it as "hey, that's jealousy" at a population level.
