When you think about the most successful applications in crypto nowadays, you will not see the most successful one because its so ubiqious that its easy to overlook. it has a market cap of roughly 700 million USD and is constantly growing at exponential rate. it is reversely correlated to the value of BTC and its ticker symbol is USDT.
USDT allows to store wealth and to transact it between exchanges without exchange rate risk. This is big. It keeps most exchanges running and not many people request proof that the backing USD really exist.
In the broader picture there are gateways that bring fiat in and then there are gateways which allow to store fiat and reuse them in the crypto currency system but not to directly be withdrawn. Tether belongs to the second category. The other cryptocurrency that has the exact same attributes is bitUSD.
For this to happen, bitUSD has to be listed on a major exchange.
Once bitUSD is listed on exchanges, it is set to become the killer application. No DEX needed for anything other than trading BTS for bitUSD. Just like as with Tethers, bitUSD that have been created once are unlikely to be exchanged back to BTS, so the price of BTS will skyrocket. The event that makes this possible will most likely be the collapse of USDT, either via investigative journalism or by a successful strike of the US authorities who will have no interest in having a private company acting as a central bank for USD on the blockchain.