The cultural narrative that's built around films starring DC Comics superheroes over the course of the past decade or so reads thusly: DC films are too dark and dour, and the company should take a cue from Marvel, whose films always leave room for the fun and whimsical elements so crucial to the superhero genre.
It's a gross oversimplification, but there's no denying the kryptonite-hard nugget of truth there: Years ago, Warners/DC executives looked at the runaway success of Christopher Nolan's dark and dour The Dark Knight trilogy, and concluded that they'd cracked how to approach the superhero genre, once and for all.
But they'd conflated the "once" with the "for all." Because of course what they had instead cracked was how to approach one particular superhero—a dark and dour one. It was a failure of insight akin to mistaking a huge forest, teeming with verdant and varied biodiversity for one lone, particularly spooky and gothic-looking willow tree.
Different heroes don't just come factory-installed with differing sets of powers and color-blocking, but with different outlooks, motivations, goals and fears. For movies about them to work, these characters must be approached in the particular narrative mode and tonal valence that best resonates with them. Spider-Man isn't Thor, Thor isn't Iron Man. Knowing this, truly knowing this, makes for effective characterization, and effective characterization means these characters can be brought into conflict with each other—delineating the contours of their hard edges by bashing them into each other, again and again, as in films like Captain America: The Winter Soldier, Captain America: Civil War and, especially, Thor: Ragnarok, a film that worked best when it gleefully and repeatedly undercut the gravid, Asgardian pomposity for which its audience has grown to know, and love, its hero.
But for DC/Warners, superhero capes came one-size-fits-all: They followed up the Dark Knight films with the similarly grim, dun-colored Man of Steel and Batman v Superman: Dawn Of Justice, a movie that attempted to draw its two main characters into a conflict that made no sense, because so little daylight could be found between their respective characterizations. Wonder Woman represented a welcome and purposeful step forward, Justice League an Olympic-level long jump backward, and Suicide Squad ... was also a movie that was somehow made and released.