I’m not sure there is a hollowing out of the middle class because it’s hard to define. For most of history, the middle class was the group of independent small to medium size business people that socialists called the bourgeoisie. It made up about 5% of the population until the class exploded in size during the industrial revolution. At some point in the 20th century the term was redefined to include workers whose income was in the middle between the rich and poor, mostly factory workers without a college education. So the decline of manufacturing jobs as a percentage of the total workforce terrifies conservatives and socialists.
