I agree with you. Proof of reserves is a good step, but it's not enough to guarantee that a centralized exchange is safe. There are other things to consider, like the people who run the exchange, how they do business, and how much money they have.
People like CZ, who believe that 99% of funds in self custody would be lost, and that funds are only #SaFu when you store them with Binance. Take note that nothing should serve as a guarantee that any centralized exchange is safe, nothing at all. Centralized exchanges do business through fractional reserve scam, they take your money and try to use it to make more money for themselves, and how can you know how much they have, and if it is enough to cover liabilities, either way you have to trust what they say, and you shouldn't. Store your funds only in a self custodial wallet.
I'm also worried that many centralized exchanges keep their insurance funds in their own tokens. This is a conflict of interest, because it gives the exchange an incentive to manipulate the price of its token.
They can print their tokens just out of thin air, so they rather use your money to either trade or gamble in other investments and see how much profit they can make from it, and if they fail and become insolvent, they print out millions of their tokens out of thin air and try to use it to stay afloat. By the way, why should you be worried about what centralized exchanges do, when you can store your funds the right way.
No wonder exchanges will always accept any shitcoins to be enlisted on their platform once they were able to reach a greed business terms and fund the project for a while, this also call for more caution for potential investors seeking for highly fast growing currencies, most of them were nothing but a hype to attract for more investors, thanks that we have the use of altcoins to differentiate bitcoin from other currencies in cryptocurrency, so CZ is as good as any average businessman and understand the way to persuade people for a business patronage using his exchange even though he knows himself that non custodial wallet is the best means of having crypto assets.