XCP-BTC trade with the DEX isn’t such a bad idea IF people are aware of its limitations (ie slowness).
Treat it more like an OTC market. Say Alice has 5 BTC she wants to invest in XCP. She announces her intent on the chat. Bob says he can sell at 0.005.
Alice accepts, so Bob then places 1000 XCP for sale at 0.005 with expiration 6 blocks (short expiration because he does not want Alice to wait and only buy later if the price goes up)
Alice buys. No waiting for Polo to confirm. No counterparty risk. No fees.
(With polo the fee is 0.2%? both parties then save around $5 by using the DEX)