You have a completely defeated being who, according to Christian theology, is nevertheless alive and well on planet earth and is doing all he can to ruin the eternal existences of as many people as possible, and is successfully seducing a lot of people into sin and damnation. That doesn't look, at least at this point, like total defeat to me. If the people who die having accepted Christ's atonement are saved, and people who die without having accepted Christ's atonement are lost, then it looks as if the devil is beating God in the numbers game.
How can this be?
Well, it's easy to see what the Calvinist answer is. But where do you go if you don't want to go there? At least you can see the argument from exclusivism to Calvinism.