> People today are MUCH better off on just about every dimension than in the 1940s!

Sure, but that wasn't the premise. Young people (< age 55) today have a far smaller share of current total wealth than young people did of total wealth in 1940.

And until 1940, each generation accumulated a greater share of value than the generation before. Post-1940, each subsequent generation has a smaller and smaller slice of the pie.