Not that I don't agree, but PKI relies on a trusted authority which can be compromised. If you're running a trustless system, basically any party can be compromised but the blast radius is limited to just the compromised infrastructure and money, not the entire system.

No, a regular database can't do that "with PKI", you have to write ledger software on top of it and you have to have one party operating the software.

cryptocurrencies are the ledger software, API, and data store layer -- and you do need trust between peers because the JPMorgan will take actions to reverse transactions if there are problems that need fixing.

It's not magical, but it is convenient for the actual ledger actions to be mathematically proven instead of the result of accounting rules in code.

What's your definition of a "regular" database? If you need a distributed, well-sequenced, auditable trail of cryptographically signed operations representing the transfer of value, that quite literally can be fit to match the definition of a blockchain.

People who haven't done it probably underestimate the incredible amount of fiddly nonsense is involved in actually writing accounting software to handle a ledger.

Banks and brokerages very often use software written 40 years ago because it's so much trouble to get correct.