This year’s Superman opens with the Man of Steel lying spent and wheezing on the Arctic tundra. It’s a perfect metaphor for the state of the world’s founding superhero after the battering he took under DC’s chaotic Extended Universe project. An uppercut from the ponderous Man of Steel (Zack Snyder, 2013), a one-two from the joyless Batman v Superman: Dawn of Justice (Snyder, 2016), a body-slam from whatever the hell Justice League was supposed to be (Snyder and Joss Whedon, 2017...