What If You Split Up Batman & Superman and Developed the DCEU?
2016's Batman v. Superman: Dawn of Justice is widely regarded as the beginning of the downward spiral of the early DCEU. Call it trying to play catch up or attribute it to the "Amazing Spider Man 2" syndrome of trying to fit in too many plot points. While there were some good things, the main plot point was often distilled and meandered the impact of them. The ambition got in the way of execution.
Imagine if you took both of these characters and further expanded the universe with their more standalone movies before you brought them together in a Justice League movie. Not to say that DC should take the Marvel route entirely. The DC movies had a grit and tone to them that made them unique. The cinematography of Larry Fong gave them their own ascetic. You don't necessarily want to be a MCU carbon copy.
The Superman story in this current DCEU was rebuilt in a grounded practicality - as much as you could given aliens and what not. Clark Kent felt like an outcast. In Man of Steel, he ultimately chooses earth in killing Zod. Then again, he kills a part of his history for a world that does not fully accept him. Man of Steel felt like a journey of someone figuring it out. Figuring out his strengths and weakness, and while the main criticism was that Superman wasn't "heroic" enough, this was a man who was coming into his own.
Based on that, there could have been a three movie arch for Superman. You could have taken the story line from BvS and made a Man of Steel 2. Most of the movie veers into the territory of 1992's The Death of Superman. Lex Luthor is too much of a thorn in Superman's side to be stretched thin in a Batman story. You can do that with an ensemble movie and the Legion of Doom later. For now, the "God Complex" that's shown in BvS could be reserved for their story.
From here, you can have Superman fighting Doomsday and ultimately dying. The death of Superman scene could have been so powerful and sad, but it takes too long to get there. Once you get to the heaviness of the scene, you are exhausted in navigating why it's important.
The connecting threads aren't really that strong to begin with. Why were Batman and Superman so antagonistic to each other? There may have been something to Bruce Wayne seeing Superman as an alien threat, but the world's greatest detective couldn't find out that Clark Kent basically lived on Earth his entire life? It came off as two guys in a "who is better" measuring contest. Clark is against Batman's brutish streak in handling criminals. Bruce has something against aliens. Rightfully so - his building was destroyed and lives were lost in the fight between Superman and Zod. Again, they couldn't have talked this out?
In the Dark Knight Returns series, Superman an agent of the U.S. Government and sent to fight Batman. This may have not come off as great within the movie either, but a little better than what we got. Lex Luthor sends fake notes to Batman and puts Superman in situations to make him look inept as possible. While the fight was cool in the heart of the comic, they draw a truce by Superman calling out "Martha" in a last gasp strain. Really?
In 2013's San Diego Comic Con, director Zack Snyder stated that he would draw inspiration from Frank Miller acclaimed 1986 comic series, The Dark Knight Return. So, why not give a full movie of that? In the Batman v. Superman realm, the psyche of Bruce Wayne is very grim and jaded. Even his reveal was more of a horror character that stalks his prey. The way he branded criminals was borderline maniacal, disregarding the pillars of what his character was based on.
There's a scene in the movie where Bruce Wayne gazes upon a marked up Jason Todd costume by The Joker. Instead of having Jared Leto peruse around in the Suicide Squad movie, he could have been the main antagonist in the Batman movie. Jason Todd could also come back as The Red Hood either as a second villain or what's to come. This would have been a perfect opportunity to introduce either Batgirl or Robin. Bruce Wayne is much older and is going to need some help this time around.
Hints of the Justice League to come was just thrown together in a montage of surveillance footage. The Darkseid and Flashpoint story lines were hinted at, but the foundation of the conflict of Bruce and Clark didn't make you take it as serious. Again, each of these things should have their moment. Once Superman dies, you can have the Justice League come together to fight Darkseid once each character is established. We can spend some time with Aquaman, Wonder Woman, Cyborg, and Flash and giving little nods to each other as we go forward.
Build some continuity. Since you would have had two Superman movies at that point, the third one would be the redemptive story showing the "truth, justice" character we all know and love. With Batman, he could either continue or pass the mantle down. Deathstroke has been teased now in the after credits scene of Justice League. He can take advantage of an aging Batman and put him in at a disadvantage in a way we haven't seen before.
In order to build a universe, the audience has to first invest in each brick. This is what Marvel did so well. It's also why Wonder Woman felt like a big sigh of relief. You were already familiar with Iron Man, Captain America, Thor, and The Hulk. They also introduced characters like Hawkeye, Nick Fury, and Black Widow in ways where the puzzle pieces fit.
While the extended version of BvS does a little better explanation wise, the movie still feels like a missed opportunity at a big moment. Too much, too soon.