if the firm managing your 401k makes a bad investment
The administrator of your accounts has zero control over most of the funds available in them, their rise or fall, and your funds are separate from any investments that financial institution may or may not have made.
If you have a 401k with fidelity, or ADP or Schwab or Trowe Price or whoever, some of those are banks, soke finance companies, some payroll, anyway, the point is for each, the money in your account is yours to allot and invest as you wish based on yhe invesrment options your company chose or negotiating with them to administer your company’s plan. The admin makes money by admin fees, not by taking your money and reinvesting it in something you don’t know about. Granted, yes if there is a stock market crash, most financial companies will similarly overall struggle, but they have lots of arms and operations (mortgage loans, commercial, consumer banking, investment banking, etc.) and they are 100% all disconnected from the money in your 401k.
That said, 401ks are awful and a sham that were pushed on an uninformed public and we’ve only just begun to see the effects as the first generation reaches end of work age…and can’t stop working. It’ll continue. Props to anyone fighting and organizing against it or trying to avoid as much as possible. System fully bought and broken by greed.