The DC Trinity is one of the most iconic and complex ensembles in the entire comic book realm. Superman, Batman, and Wonder Woman all work together for the greater good, and their dynamic has become a genuinely fascinating narrative that has engaged readers and audiences for decades. However, the fact that they work together doesn't mean they're the same, and in the special features of Wonder Woman's home release, comic book writer Greg Rucka explained that Diana Prince's morally gray relationship with violence is what makes her so distinct from Batman or Superman. Rucka said:
They all have very different relationships with violence. Batman is traumatized by violence to such an extent that he wants to control it. Superman's power set is such that his relationship with violence is you've got to hit him so hard for it to matter... The way you get at Superman is emotionally because you're not going to beat him by pounding him down unless you happen to have Kryptonite. Diana comes out of a warrior culture that knows what that means in every sense. Diana's never going to enter into combat without knowing exactly what it is she's about to do. Her skill, her discipline, she never goes to the sword first.
Unlike Batman or Superman, Wonder Woman trained to become a warrior since her days as a toddler. She comes from a culture that understands the weight of death and combat, but she's also prepared to unsheathe her sword and take a life if a conflict escalates to that point. While Batman (most incarnations, at least) will stop at nothing to save every possible life, and Superman is so invulnerable (unless you have Kryptonite) that the idea of sustaining physical damage often doesn't even register in his mind, Diana sees both sides of violence -- understanding when to instigate it, and when to stop it.
This idea arguably makes adapting Diana Prince to the silver screen easier, as well. As Wonder Woman placed Diana firmly in the trenches of World War I, it established her willingness to kill (when necessary) while keeping her firmly identified as the film's hero. By contrast, recent stories centering on Batman and Superman have often found themselves bogged down by the moral debate of whether or not The Dark Knight or the Man of Steel should kill. Wonder Woman doesn't suffer from that problem (at least not to the extent that the others do), and her solo movie effectively sidesteps the debate.
That idea continues to work so well because Wonder Woman essentially represents a perfect marriage between Batman's overwhelmingly human faults and Superman's unnervingly perfect, godlike status. She brings Bruce Wayne back from the brink of darkness with her inherent sense of hope (which is something that we have already seen in the DCEU), and her connection to Clark Kent effectively keeps the world's most powerful hero grounded. With all of DC's heroes about to unite for the very first time in Justice League, something tells us that these qualities will only make Diana more relevant as this franchise evolves.