It doesn't account for obvious confounding factors to prove it's conclusions of stagflation. Comparing parents to children has a pile of variables during this time frame that the article doesn't examine in the slightest.
For example it doesn't mention birth control once.
"50% of people today make more than their parents."
"90% of people 60 years ago made more than their parents."
If yes, what is the problem that you have with this study again?