DEX is not a solution of that problem. While the exchange is decentralized, user and his funds are still centralized.
Why are funds centralized on decentralized exchanges? I doubt you understand how decentralized exchanges work. Exchanges like Cryptopia play the intermediary role between the buyer and the seller. (Real) DEXs allow to do a trade without intermediary and thus, there is no centralization.
I recommend to read this article
https://coincentral.com/dex-decentralized-exchanges-explained/