For crypto to be a successful currency, it needs to have a stable value. The Argentinian peso looks stable relative to BTC as its 300-1000% volatility relative to USD is sky-high. If I buy an iPhone for 1 coin, I don't want it to depreciate and be 10 coins next year neither do I want it to cost .1 coin. Apple would be pissed in either case since it would involve a lot of new contracts and wages and it would add to the cost of doing business. Stability is why Central Banking is a hard thing to do. No one complains until there is instability.
Stable coins, on the other hand, are a real threat. A Trojan horse that may eat away market share from Central Banks in the long term. Currently, when $1 is used to buy a Circle USDC coin, USDC deposits $1 in a bank account or a securities dealer's bank account and the $1 enters the USA banking system and is part of broad money. Seems normal.
No big deal yet, but coins are growing very quickly, Money supply from USCD is backed by the growth of the crypto economy, not real business cycles. But they will become big standalone currencies targeting a fixed exchange rate. A piece that is outside traditional bank purview.
It will be a major problem for countries whose currency is less stable than the US dollar.
Still, the problem of money supply outside a Central Bank's control remains.
I guess the best way to make money in coins is not in coins are stable coins but watching marginal currencies replacement by stable coins.