I will say this is as good a time as any to admit I always wanted the writing chops to write a "mainstream" DCU take that starts off in as jaded and cynical, gray and hopeless, a world as you can get and it gradually turns through sheer force of sweat, blood, tears, will, and hope into the optimistic world the DC heroes inhabited until the Dark Age of Comics. Including all the attempts at "grounding" or "making realistic" or "Snyderverse" as the starting point. Or like it's almost like an analogue horror look into it at the beginning. Like...
Well it works because DC's the long-history universe and you can root a lot of this darkness in pre-Superman publicity vigilantes and whatnot. Have the suicide squad, vigilantes, etc. all exist. Perhaps, in the interim between the JSA retiring in the '50s and the rise of the modern age with Superman/Barry Allen/etc., the original silver age Suicide Squad and similar "super agent" types were sacrificing themselves to save the world. Maybe, those guys are all gone now. The JSA's mostly retired. The world is dark. Somewhere, the last green martian was transported to Earth and has been wandering this world. Somewhere, Niles Caulder gets crippled, John Constantine fucks up, etc. Bad things happen.
-People do freak the fuck out seeing superheroes with clear physics-bending superpowers. The aliens, the gods, the science-bending, all of it.
-When The Bat-Man comes aboard people flip the fuck out at him endangering a goddamn little boy in what looks like a circus outfit. Same for when a little boy is following Flash at his speed. Or why there's a group of teenagers now, society is really fucked up with children being regularly endangered.
-Lex is indeed that seemingly untouchable CEO the way people argue Musk is and it's obvious he buys up love yet everyone knows he's a corrupt piece of shit. He built Lexcorp from nothing. He really is that peak human. Who can stop him?
-The actual horror of Gotham being that dangerous but everyone's too poor, or too tied down, or the rich and glitzy is still JUST worth the enticement.
-The scientific horror of the Speed Force being comprehended, or alien tech like the GL ring, or these heroes claiming they're what are straight out of Greek myth and actually look it.
This could work, have the JSA exist as "historical legends" at this point. The "newsreels" of them being treated as "propaganda". After all, they all seemingly vanished after 1953.
Also, throw in the rest of the fixings. Simon Stagg, Niles Caulder, etc. Plenty of rich assholes with questionable motives. Maybe, in the midst of it all, we get some "true believers". What if Perry White remembers being saved by Alan Scott or Jay Garrick as a lad and knows the heroes to be real. What if, there's always some sort of increasing revival as more and more of these figures come to light. People who were saved start to speak out. Perhaps that Man of Tomorrow really is a good guy, eh?
But ,anyways, heroes come to light again. It's like a ripple effect.
But. But...
-People begin dubbing them sarcastic names. The Man of Steel. The Dark Knight, Boy Wonder, Dynamic Duo. But they soon become less and less sarcastic. Then beloved. Then everyone knows who you speak about when you write those names down.
Epithets are a tradition going back to Homer and beyond. It's a great part of superheroes.
Let's say, Perry White or Lois Lane or someone similar begins to use them in the modern era. It gets revived. Perhaps, someone looks up old golden age newsreels and also begins to use those epithets too.
-Makeshift costumes give way to real ones. Iconic ones. Symbols get thrown on T-shirts. Symbols become symbols.
Symbols pop up more and more. The original era of golden age heroes gets seen in public once more. People begin to look up in the sky. Some old man remembers stories of a local masked do-gooder and sees the same man pop up, barely aged past their '40s. It's not just the JSA. Uncle Sam, Plastic Man, and endless veteran heroes pop up once again. The first appearances of the big 5 of the JLA trigger an endless ripple effect across the planet.
-They save the day. They keep saving the day. They band together to save the day. People can't believe it keeps happening. Then, finally, they do.
Yeah, that's how it goes.
-The young generation of heroes go from the idea of endangerment and how desperate society is to keeping the promise of tomorrow alive. That even the generation of tomorrow can evoke positivity and change now.
Somewhere, Wildcat's too stubborn to remain retired. He puts on the old suit and is the first one in a ground-zero brawl with someone way out of his league. The Superman generation sees him and, somehow, he's recognized from old stories and newsreels and clippings. Perhaps Black Canary recognizes him, who knows. The old guard come out of retirement more and more. The children join in.
-Lex isn't just busted by Superman and his liasons Clark, Lois, and Jimmy. He runs off. He changes. He becomes the most dangerous man in the world. A man who's so intent on imposing his will he leans into the opposite of the man he hates so much, the "supervillain." The man who casually builds superweaponry out of scraps and confirmed to be far, far, smarter and dangerous than anyone ever realistically comprehended, indeed, the most dangerous man in the world... and yet.... he never wins because there's a man who can match him and go "no". As Elliot S! Maggin put it: “In another place, under different circumstances, this man might have been a Caesar, a Napoleon, a Hitler, or an Archimedes, a Michelangelo, a da Vinci. A Gautama, a Hammurabi, Gandhi. But in this place, at this time, he was more. Superman made him more.”
It'd be interesting to see Luthor's downward spiral. Perhaps, early on, Bruce or someone similar tries to get an understanding if they can shift and reform him. But Luthor's ego is too far gone. This isn't someone with the innate good that Bruce, or Ted Kord, or any number of heroic rich guys has.
-Gotham changes. It becomes safe. Criminals huddle under the strong in a dwindling attempt to keep control, and the strong, try as they might, cannot stop the Dynamic Duo of Batman (no longer The Bat-Man) and Robin. The supervillains attempt to make chaos, they attempt to terrify and horrify and make people give up in genuine, shuddering fear... and yet they go down, always go down, to someone more terrifying than they. And he terrifies them. The one they whisper of in shadows so he won't hear them. The one that scares the scary.
One day, they find out that not only is he real, he's got friends.
-The impossible and the superhuman, the peak of human potential... once so scary, begins to seem different. Something to aspire to. Something that can be turned to good and to benefit others, society, humanity. Technology advances, ages upon ages in a decade, as people try again.
At this point, you'd show some legacy heroes in their pre-mask days. John Henry Irons, Ted Kord, Mister Terrific II, etc. Perhaps also show the JSA's offspring in their pre-hero days too. Jack Knight, etc.
-People open their eyes. They start to rebuild themselves. Society. Things change. The world is colorful again. People do what they can. People smile.
Despite it all. Heroes will die. Dan Garrett, Terry Sloane, The Original Doom Patrol, etc. But the world hears about it and honors them. Keep Valhalla Cemetary, it was a nice bit of worldbuilding that the heroes have a cemetery dedicated to their fallen. Perhaps the Doom Patrol go out in the way it's seen in the Batman BATB series. The various monsters, magic, and hidden projects the world's powers have tried to hide start slowly coming out too.
-In short? As the quote goes, they were made to believe a man can fly.
Baaaaaaaaasically make a perception of a world of superheroes that is Marvel-esque at first and indisputably becomes classic DC by the end of the tale.
This isn't just Marvel-esque at first. You'd really need to make it a crapsack world. Kinda just make our IRL but even more demoralized. There is no hope, no nothing. It's all cynical and nihilistic.