Banks also have control of their own ledgers and can just issue a reversal transaction. If it's between two banks, it'll be more complex, but overall that's still the case

companies that accept different cryptocurrencies

But this is the issue, that's like 0.0001% of possible places you can use your funds (probably I'm way too generous with that number), and none of it to not die from hunger, cold or dehydration.

And the volatility is still absolutely absurd for something to be used as currency, like all other Cryptos it is dominated by instability and speculation to an excessive degree.

What that statement ment was, that you can't use it to invest and diversify you portfolio if its not in an exchange. So unless you keep the majority in the exchange, you can't trade it without paying the transaction fees every time.