Actually base on my personal experience One of the decentralized exchange EtherDelta was also compromise in 2017 at that time im doing trading when it suddenly shutdown i was afraid that my account was also compromise since im using my private key and not using metamask But luckily it was repel and the DNs was not compromise thats why even a DEX has flaws and vulnerable to any attacks so for me Decentralized or Centralized exchange still vulnerable. Im using Binance for my day trading activities and im glad that Binance was stored most of its crypto in coldwallet for more safety. im using both DEX and CEX so im not bothered with who's more secure or not!