Cash is absolutely used as an investment scheme, by forex traders, by people in other countries to hedge against the weakening of their currencies, by foreign governments and banks. This is encouraged by the US deliberately as an effect of the petrodollar.
Nominal terms amount to how much of your investment in dollars you lost (or gained) while holding dollars, in real terms. Real terms are all that matter.
Cryptocurrencies are also used to trade for other stuff, as is their stated purpose.
They both have the same characteristic that makes one a pyramid scheme, but somehow not the other. They're fundamentally similar assets, but for some reason one is given a special category carved out specifically for it that actually does not exist. When you take away this special status that is only ascribed to fiat currency to differentiate it for the sake of discussions like this, they're interchangeable assets that share all fundamental characteristics. All fiat currencies are speculative assets.
Now you're talking about foreign currencies. Yes, foreign currencies can be traded for speculation purposes. When a speculator invests in a foreign currency, they think that the currency will appreciate in the future. The important fact is that currencies appreciate and depreciate according to international trade and a whole bunch of other factors unrelated to speculation. The speculator does not rely on other speculators buying the currency for it to appreciate and making a profit. Therefore, speculation with foreign currencies is not a pyramid scheme. This is in stark contrast with crypto-coins, because unlike the demand for foreign currencies the demand for crypto-coins is mainly fuelled by speculation. The only non-speculative uses of crypto-coins (as far as I know, ransom payments and purchasing of illegal substances) constitute a tiny minority of the trading volume. Therefore a crypto-coin investor absolutely depends on other "fools" investing in crypto-coins at some later time in order to make profit. This is confirmed by the fact that they're constantly trying to talk other people into buying crypto-coins, which is never the case with fx speculators. When they run out fools, they will no longer be able to make a profit. And this is why crypt-coins are a pyramid scheme and international currencies are not.
Nominal terms amount to how much of your investment in dollars you lost (or gained) while holding dollars, in real terms. Real terms are all that matter.
Cryptocurrencies are also used to trade for other stuff, as is their stated purpose.
They both have the same characteristic that makes one a pyramid scheme, but somehow not the other. They're fundamentally similar assets, but for some reason one is given a special category carved out specifically for it that actually does not exist. When you take away this special status that is only ascribed to fiat currency to differentiate it for the sake of discussions like this, they're interchangeable assets that share all fundamental characteristics. All fiat currencies are speculative assets.