Neither we should trust DEX smart contracts to store them for too long time. As at least when we trust CEXes, they get sued after messing up, You can't sue a faulty hacked smart contract. And what comes to praising decentralization in general, it almost always has centralized elements. Like wrapped btc that just got depegged supposedly because of
Almada Research minted it a lot.
DEX also cannot be fully trusted, because some DEXs are managed by scammers who will easily take our assets. As you said, no one can sue Smart Contracts if they commit fraud and take the assets of the users, they will just disappear. In contrast to CEX which will be demanded by its users directly. The main security is actually in its own use. they must be aware that crypto is very risky, and must be really good at keeping their own assets safe. A personal wallet is a safe place that can be managed alone.