Are you sure? What is the 401(k) exposure to "AI" related stocks and broader market shocks?
All of this is kind of beside the point though, because the issue was leverage not exposure. In south korea ppl were forced to sell at the low point of the market due to margin calls. For a retirement account, you can just choose to take a disbursement next month or next year (assuming youve managed personal cash flow with sequence of returns risk in mind).
Systemically i guess thats more a question of 1) is US equities just an AI trade, and 2) how much of all these investment vehicles are just such assets. Regardless of the answers, the nice thing is that unlike debt, there isnt a positive feedback loop here (i.e. margin calls increase volatility)