Much of the 2007/8 crisis was caused by derivatives and other margined (leveraged) financial contracts between banks and other institutions
meaning there were huge liabilities that were not well understood, or even understandable (no global ledger or database, public or not). When the crisis hit, no one knew how exposed anyone else was and thus nobody wanted to extend credit to anyone else, margin requirements went up, and margin calls got more urgent.
Given time, things were nowhere near as bad as you could have been forgiven for thinking at the height of it. But the risk created by the fact nobody knew that caused the credit “crunch” and liquidity to dry up, and while banks were bailed out and recovered, the downstream impacts were horrendous.
That scenario simply isn’t possible even with the craziest, risky-as-shit defi protocols. You can see how much is at risk in every contract for every address, reports could be built automatically, and the risk is defined by the code, there is no ISDA agreement or OTC contract that might cause someone to come along and say you actually owe a bunch more money than you put at risk, and every cent (or satoshi, or whatever) of collateral is accounted for.
So it’d have helped a lot. Albeit the whole financial system would look quite different to how it does today (that’s the goal!).
Also, although the general principles are good and the primitives are increasingly in place, the protocols (financial products) in defi are mostly still “toys” and not, for the most part, ready to replace the current system. There is no technical reason why they can’t though, and progress in that direction is happening even if a lot of defi doesn’t make it look that way.