Is the age of “Watchmen” dominating the comic-book conversation coming to an end? If DC Comics creative chief Geoff Johns has his way, it just might be.

Superheroes were never the same after DC published the seminal “Watchmen” in 1986 and 1987. The comic, written by Alan Moore and drawn by Dave Gibbons, is a blistering satire of cape-and-mask-wearing avengers, suggesting that the four-color heroes would do more harm than good if they were real. The graphic novel is routinely hailed as one of the greatest comics ever, its influence...