All other forms of holding wealth.

If I buy Apple stock, I have a piece of a company that rakes in billions in actual profit by turning raw materials into useful machinery.

If I buy a US bond, I get interest, and it is guaranteed by the full faith and credit of the United States.

If I buy gold, I own a physically rare and hard to counterfeit asset that humans have valued for thousands of years.

If I have a savings account, I get interest, and the money is guaranteed by the FDIC.

Even dollar bills under the mattress don't decrease in value by 10% in a single day.

Sure but your dollar bills under the mattress do not increase 70% in value in one year either. Volatility is not necessarily a bad thing, it means cryptocurrencies are growing. There is a good chance they will stabilize eventually.

If you own, say, ADA and stake it then those staking pools run smart contracts.

Except that gold could be used for industrial purposes, so hoarding it is not only useless, but harmful.

Stocks because (you own part of a company which has assets and/or produces income), real estate obviously.

> Stocks

At current valuations (Shiller PEs ~40), stocks are disconnected from their income. Therefore, if the Fed tapers harder or even reduces the money supply, it will crash. This leads to a "Ponzi" musical chairs aspect where investors getting in last will have bailed out the ones before them.

> Real estate obviously

Valuations are still heavily influenced by monetary policy, but also by intrinsic scarcity. As space runs out around desirable areas, the ways to acquire are increasingly limited to buying from an existing owner.

Right but what effect do stocks changing hands in the stock market have to the company? Perhaps if you had enough of them you could influence the company's direction, but it's the same with some cryptocurrencies.

But for the average retail investor owning stocks is the same Ponzi, no?