You're right, stablecoins held custodially in an entity could be subject to similar contagion.

Yet, non-custodial holding is becoming much easier and safer.

Crucially, wallets are improving a lot, and a spectrum of custodial options is developing, with rich tradeoffs in eg. safety and self-sovereignty.

For example https://www.coinbase.com/blog/how-smart-cryptography-makes-c...