The Nolan Trilogy broke DC's brain. They took away all the wrong lessons from it. They mistaken "Grounded, bent of realism" for grim/dark when that wasn't actually a thing in Nolan. It's like saying Keaton Batman was grim/dark when it was Gothic.
The trilogy isn't a interconnected universe and it was never meant to be. Watch any of the 3 films and you have a self contained complete stories. You don't need Begins to watch Dark Knight, Begins doesn't need DK nor does DKR need any other. You don't even need to know anything about Batman to enjoy any of them. Yet they can be viewed as a trilogy, it's both.
Man of Steel the first test of new DC movies post Nolan showed how DC was never going to put out a good movie. They didn't know why Donner Superman worked and grim/dark is being dark for the sake of being dark, some times literally with awful lighting. They also have no idea how to make a good movie in general. MoS first act is pointless, who cares about Krypton. All we need to know it blew up. Superman 2 doesn't setup Zod in their own act. Donner didn't need to as the title of General and his callous actions on earth informed us of who he is. His past died with Krypton as much as it was for Kent, it doesn't matter. Who cares if you see him try to start a coup, it's irrelevant.
Another big thing is Donner and Nolan doesn't punch the problem away. Supes punching a Nuke isn't helpful. Nolan has to detain Joker and sacrifices himself to stop Dent. Dent only shoots a couple people and they arguably deserve it. The threat is emotional, the legacy and justice Dent was. Joker's threat is an idea, an idea he uses to undo people. Supes doesn't punch Zod to submission, he has to be clever. The threat from Zod isn't planetary destruction with some machine of pillar of light, it's your compliance and if he has to he will personally get it.
Marvel does get around this problem somewhat by making the punching a little bit clever. They still punch
alot of problem away via minions and each other but the coup de grace isn't quite that. Avenger 1 Tony "Sacrifices" to close the portal, they don't punch the portal away. Yes it is a nuke, but it is how they use the nuke is the loophole. Iron Man 1 opening is the same but reverse. Tony works towards punching the problem, the cleverness is before the punching. Nolan Batman has to be clever to solve the problem.
Superman Returns has problems but punching isn't one of them. It's why when he uses his powers it is epic and meaningful. Him having to rescue Lois is tense and it's is very real to Lois therefore is toe supes. He doesn't instantly save the day, he has to think, he has to be clever and it ends with that Donner "I will show you a man who can fly" where the crowd absolutely goes wild like it would in real life, seeing something amazing and that bleeds into the audience, it's pure. Capping it with airline safety is just amazing.
Donner, Nolan didn't make Superhero movies, they made movies that had those characters but treated them like they didn't have a cape. You would have to tone things down a fair bit but Batman could have been an ex-cop who after some trauma fights crime on his own terms yet have the same beats as N/Batman did. Superman didn't need to be Kryptonian. They use them as enhancers, visibility, to jump start the movies, waste little time on the origin story. N/Batman transcends Batman into legitimate movies as does Donner. Like Blade or Death of Stalin would you have ever guessed it came from comics if you knew nothing about them?
but that doesn't address the concern of them repeating "Thanos" vs the Avengers Justice League, only with much less build up and fanfare.
Should they still proceed with Darkseid, as stated in JL or should they swerve and do Starro or Bizarro or Braniac or whatever other big villains they got before diving straight into Darkseid?
If they can make a good movie with Darkseid, that has more reason to exist than "We planned on Darkseid showing up" then go for it. I don't think they can. I don't think they have any motivation for a new Justice League movie period.
**** Darkseid. All the above states why you shouldn't use him. They don't have anything built up, everything they have is a dumpster fire. They shouldn't even be thinking about Darkseid or crossover or any universe or huge villain.
They need to dump being edgy, epic, emo, dark and abort everything that came before. They need to stop being reactionary. They need real proper respectable directors, another Nolan to jump start DC so people actually want to see DC movies instead of rightly expecting another **** show. One they have their credibility back they can make other standalone movies and have no expectations to turn it into a trilogy or even a sequel. I cannot empathise how much any new movies has to be stand alone for them at this point.
DC transcending the genera is what would get them out of the hole they dug themselves while Marvel gleefully buries them. They need to be like Nintendo who got out of head on fights, not to tread the same ground. The animated movies shows how it can be done.