> If the S&P 500 dropped 20%, that's about a year's growth.

But the S&P 500 is currently trading at over 2x its average long-term CAPE: https://www.multpl.com/shiller-pe

So it can reasonably be expected to drop more than 50% to return to average long-term valuation levels.

And the "nonfinancial market cap to gross-value-added" ratio is even more insane, I have a site tracking this number: https://sharperatios.com/market-cap-gva.html