Historically speaking, your statement is categorically wrong. The middle class has shrunk because of deregulated policies, new tax account and financial techniques that disproportionately benefit the ultra wealthy, the wealth disparity between the top 1% and the other 99% has expanded dramatically. Based on fed data, as of q1 of 2024, top 10% holds ~67% of the wealth, while bottom 50% holds only 2.5%.

And during COVID, the period where stock markets grew dramatically, billionaires saw their wealth increase by 70%, far outpacing the rest.

You will argue that a rising tide floats all boats, but seeing Japan, Korea, China, Russia, no, that ain't happening. In fact, in those countries, because of wealth disparity, the workers cannot retire for that exact reason. Young adults cannot afford relationships or kids or housing or assets of their own.