There is a huge problem with the collateral model: liquidity.
If you put up $X in FOO_COIN as collateral and FOO_COIN starts tanking in value, the contract is supposed to auto-liquidate once it hits a certain point. But there is absolutely no guarantee that this can find a buyer. So the "guaranteed" collateral recovery is not exactly guaranteed.
That's why you can only borrow up to 80-ish% of your collateral, and that's getting very risky for the borrower. It also means that the sane lending protocols are somewhat stingy with what they take as collateral and then set the borrowing limits and liquidation thresholds fairly conservatively.
When the market starts making big moves downward the liquidation bots have a keen eye on which positions are at risk, watching and predicting the oracle updates, and within a block or 2 (~30 seconds) of a position being vulnerable have the deal all closed out. It can even be all done in a single transaction bundle that calls the liquidation function, pays back the debt, takes the collateral, and sells it on a dex, all in one go.
The market price for the collateral would have to drop more then 20% in the span of that 30-seconds for it to not be profitable for the liquidator.
That's not to say it's impossible for this to fail, the biggest and sharpest dumps happen during liquidation cascades. But a failure is in the category of 'black swan event', and not something that is seen with regularity.
A "black swan event" is something which was obviously possible in retrospect, but no one could have predicted other than via blind guessing. If you can explain how it'd happen in advance, it's not one.
It's actually a correct use of the term. A “black swan” is something that is believed not to be possible – or, in retrospect, something that was believed impossible but happened anyway.
The term predates the discovery of black swans;
> However, in 1697, Dutch explorers led by Willem de Vlamingh became the first Europeans to see black swans, in Western Australia.[9] The term subsequently metamorphosed to connote the idea that a perceived impossibility might later be disproven. Taleb notes that in the 19th century, John Stuart Mill used the black swan logical fallacy as a new term to identify falsification.[10]
There are a lot more backstops. Traditional finance can have this problem, but we can install human systems to limit the blast radius of things. As you say, it is traditional finance on steroids.
Crypto enthusiasts seem to think it is the opposite. People tell me that defi loans are "zero risk" because of the automatic collateral systems and I just laugh and laugh.
Crypto finance and especially DeFi is tiny compared to traditional finance. The blast radius is still small without the regulations. But the regulations will come. Crypto finance is going down the same path that traditional finance did just in a period of a few years than a century.
Everybody who claims there's "zero risk" is either lying or blind to the risks. You can't get those large yields with zero risk.
If you put up $X in FOO_COIN as collateral and FOO_COIN starts tanking in value, the contract is supposed to auto-liquidate once it hits a certain point. But there is absolutely no guarantee that this can find a buyer. So the "guaranteed" collateral recovery is not exactly guaranteed.