WARNING: The following contains spoilers for Zack Snyder's Justice League, now streaming on HBO Max.
In the early stages, just like the Marvel Cinematic Universe, the DC Extended Universe was all about growth and development of characters. Superman had to navigate his powers, Batman had to let go of his rage, and Wonder Woman had to embrace her connection to humanity again. These character flaws continued with the inexperienced Flash, as well as Aquaman, who didn't understand the value of teamwork, but just like the Avengers, it was about the team uniting against a common threat. However, in the wake of Zack Snyder's Justice League bringing them together, there's one hero who doesn't even attempt to help the League, making him the worst of the bunch in the DCEU.
The film reveals that Snyder had one more hero who was cut from the theatrical version, and it's Martian Manhunter, who's the true form of General Calvin Swanwick. This comes to light after he visits Lois Lane disguised as Martha Kent, and Lois is unaware it's him. He urges Lois to get back in the world and fight as a journalist, but him not coming to her as his true self makes little sense since he believes she's a trusted force for good.
She's proven since Man of Steel she's an ally, and they could have helped each other out. However, by failing to reveal the truth, he could be placing her in danger, which makes him feel like a careless hero. Viewers understand this is to move the plot along and get Lois to Superman's resurrection, but it's sloppy as it makes Martian Manhunter a cosmetic plot device that doesn't come off altruistic at all, especially when one looks back at the past films.
It's weird seeing him with repeated opportunities to come forward to lend emotional support to Kal-El, a fellow alien who's made Earth his home, yet he leaves him alone to suffer. He's the only one Superman can possibly relate to about this part of his identity, which makes it even more off-putting that he retroactively tries to help Lois after Clark's death. Had Martian Manhunter stepped up earlier, the battle with Doomsday might have also gone differently, so Superman could've potentially survived that.
Secondly, he doesn't feel like a hero when he visits Bruce Wayne at his lakeside home, which is his second appearance in Justice League. He tells Bruce he's ready to join the fight after the battle with Steppenwolf because the League is now together, but this is a terrible way to show support. In fact, he has no sense of timing, as he didn't even help during Zod's invasion. Even after, he could have shared insight about the cosmos, yet he kept playing his role as another cog in the military, holding back crucial information that may have helped in Man of Steel, Batman vs. Superman: Dawn of Justice or Zack Snyder's Justice League.
If he were more proactive, the League might have assembled beforehand, reinforcing Earth for Steppenwolf, especially as he has intel on the Anti-Life Equation and Darkseid. The point is, Swanwick's front and center for the two major invasions in the DCEU and does nothing, unlike Diana, who was close to the Doomsday incident and decided to come out of the shadows. Even her reappearance could have inspired him, yet he opted out, cementing him as a reactive and poor attempt at a hero who now wants to jump on the bandwagon.
Zack Snyder's Justice League stars Ben Affleck as Batman, Gal Gadot as Wonder Woman, Henry Cavill as Superman, Amy Adams as Lois Lane, Jason Momoa as Aquaman, Ezra Miller as The Flash, Ray Fisher as Cyborg, Jeremy Irons as Alfred Pennyworth, Diane Lane as Martha Kent, Ray Porter as Darkseid, Ciarán Hinds as Steppenwolf, Jesse Eisenberg as Lex Luthor and J.K. Simmons as Commissioner Gordon. The film is currently available on HBO Max.