Yes, families are better off not only compared to 1979, but also 2000.
I am unclear where you are seeing family-size as a debate issue for this study. Certainly family size dropped dramatically from the 50s to the 80s, but there has not been much change in the last 23 years. The average family size was 3.14 in 2000 and 3.13 in 2023. I don't think a drop of a hundredths of a point changes the results much. Do you disagree?
I think your point of "people making good incomes feel they are not able to keep up with Blackrock as their next door neighbor" is accurate. That is why the rhetoric from Warren/Sanders/Talarico is appealing to some. The need, for some, to keep up with the Joneses is strong; ....instead of just realizing their economic position, for most, is much better.
I think the main driver, as pointed out in the article, is the significant increase of working women. A good counter-argument to that article is even though two-income families drives family income growth, but can make families feel more stressed...and increase certainly expenses like daycare, vehicles, gas, food (more eating out), and home care. The houseclearning industry has surged in the last 20 years.