The HDI ranking has been published for 36 years now. And for many of those countries I would feel confident claiming the trend goes back to at least WW2, altough you would of course have to use other, contemporary metrics to support that to get a rigorous analysis.

If the initial step in your theory about human wellfare is to selectively ignore the last 35 or 75 years of history in the highest wellfare countries on earth, I think you should at least consider the possibility that your theory might be somewhat out of date.