Bitcoin transactions can cost up to $30 US dollars. Bitcoin is absolutely not free to use.
In El Salvador, the lightning network is utilized, offering transactions at minimal expense. On-chain transactions can be costly, but they shouldn't be relied upon primarily. This is not only due to their expense but also because they are not conducive to efficient point-of-sale electronic debit payments due to the nature of 0-conf. Despite high fees, using Bitcoin can be less expensive than traditional banking charges sometimes.
If they aren't on-chain transactions, then they aren't decentralized, and they aren't actually Bitcoin. You might as well just use a bank.
Credit card transactions are rarely more than a dollar or two, and take no more than a few seconds.
Bitcoin is absolutely unsuitable for mainstream transactions.
The argument doesn't seem very valid, considering that developing countries are the primary users of Bitcoin as a currency.
No country in the world uses Bitcoin as a mainstream means of transacting--because to do so would be a practical impossibility.