How do you define middle-class, and what data set confirms that it's disappearing?
Most of the data that I've seen tells a different story depending on the statistical categories that the analyst chooses. "Households" seem to be a favorite despite the fact that the composition of the average household has changed significantly over the interval being considered, a household for demographic group A isn't the same as an average household for group B, the quintiles being compared don't contain the same number of people, the composition of the average income (money-wages vs benefits vs subsidies vs tax credits etc) differs between groups and quintiles, etc, etc, etc, etc, etc, etc.
Below for example, you've got the same data, parsed with different statistical categories.
Agree with your sentiments about the current national hardships vs the depression though.
BFD. There is a little thing called inflation to consider as well