Its specific to the kind of blockchain/DLT that it runs on. If you use an DEX that doesn't rely on miners who can pick Tx then you dont have this problem. For example the XRPL DEX does not allow any party to pick which order to execute. There is also no mempool where someone could look for bundles of Tx. A DEX order is, once submitted, added to the state of the ledger (added to the blockchain) and executed as soon as possible.