In my opinion, decentralized exchanges are not really decentralized as the token contract they run on make them equally centralized as "centralized" exchanges...

Basically you can't withdraw directly from decentralized exchange as it doesn't use real wallet of destination currency, instead it uses wrapped token that is mapped to equivalent amount of real cryptocurrency.

In the same way, cryptocurrency balances on centralized exchange are just numbers stored on a database, when you withdraw, the exchange needs to make sure it has adequate balance on hot wallet of the destination cryptocurrency.

As such the claimed 1:1 mapping is inaccurate in the same way as value of other tokens implemented as smart contracts. There is always need for another cryptocurrency to pay the withdrawal/network/transaction fee.