Correct, this is fundamentally the oracle problem. There is no link between the blockchain and the real world which is why only money-like instruments have been successful for whatever value of success this constitutes.
First of all, wut. Second, that's irrelevant because stable coins rely on fiat backing (ostensibly) so you're stacking a new problem on top of what you perceive to be a different problem. If you believed that to be a problem then stable coins give you that problem twice as hard. And a whole mess of new ones too, like zero recourse against the newly intermediated offshore issuers in low-or-zero regulation locales.
