Even if it's collaterized that's true. Even for overcollateralized ones like Dai? There's an arbitrage mechanism that forces the overall backing to be greater

Even if it's collaterized that's true. Even for overcollateralized ones like Dai? There's an arbitrage mechanism that forces the overall backing to be greater than 150%. Now it may perhaps be somehow conceivable that the value of the backing drops by more than a third within a single block, but that still makes it an order of magnitude more stable than banks, which usually operate with ~5% equity (and that's post 2008 regulations, and based on rather optimistic book values; the market capitalisation is often significantly less).