no, I think your understanding of a bank is incorrect. Yes, a mutual fund is just investing in the stock market. But a bank account is just allowing a bank to take the risk for you - they will guarantee that you cannot lose any money, but they are not actually physically holding that money in a locked safe. They invest in the stock market too, and give you a small return while they make money off of your money, and can always move money around so that whenever someone needs access to their money, they can provide it. But it's all just numbers. There's no gold coins waiting in the back.

And the point is, all this investing is going into other rich people's pockets. People who don't have public companies or stock market portfolios are not gaining from it. The "economy" does well and for rich people this means their money grows, but for poor people it doesn't mean that much. Middle income people who might have a small retirement fund or something can feel hopeful with the stock market going up but it still isn't changing their life - just a number on a screen the slowly rises. If it didn't rise as much but they had stability through public means, they might be more secure.