The person you are responding to is not arguing there is not a use case for crypto in cases like this.

They are arguing that stablecoins, specifically, require an off-chain entity that ultimately control them. And if you have an entity actually in control, why go through the trouble of blockchain? Then you can just have the controlling entity run a normal non-blockchain ledger.

I like the argument elsewhere in this thread that the actual reason is that it allows running a bank while pretending it’s not, bypassing regulation meant to protect depositors.