I think the diagnosis is accurate. The middle class is shrinking at an alarming rate. The concentration of wealth among the top 5% over the last 30 years is staggering.
However, the conclusion that it is related to globalization is unclear. Correlation and causation are two different things. I’m not even sure that a good case for correlation has been made.
There is much stronger correlation between the decline of the middle class and concentration of wealth among the top few percent originating with the fiscal and regulatory policies of the 80’s.