Warning: Contains SPOILERS for The Batman.
A scene detailing the Joker's history with the Dark Knight was cut from The Batman, and it's better without that deleted scene. One of The Batman's biggest reveals comes late in the movie, with the appearance of the Joker, played by Barry Keoghan. Director Matt Reeves keeps the Clown Prince of Crime deliberately hidden in the darkness of his Arkham cell, with only the slightest glimpse of his scars and green hair, albeit its enough to make it clear who the prisoner is supposed to be.
The Joker having such a minor role in a new Batman movie is a surprise, and it was almost a little bigger. Reeves has confirmed a cut sequence that would've introduced viewers to the iconic villain earlier in the movie, as Robert Pattinson's Batman looked to deal with the threat of the Riddler and learn more about how to stop him. That would've involved him heading into Arkham to talk to his old foe, and The Batman's deleted Joker scene would've revealed their past, with the clown commenting that it was almost their "anniversary."
The Batman's deleted scene confirmed Batman had put Joker in Arkham, which would've radically altered the movie even in a short sequence of events. There's almost no question that the scene itself would've been done well, given how good both Pattinson and Keoghan are as actors and in their respective roles (or at least, based on Keoghan's previous form and what little is shown of him in the movie). Nonetheless, it's for the better that The Batman's Joker scene was deleted, since it allows the focus to remain on the Riddler as the film's main villain, which the scene likely would've risked overshadowing.
The Joker is the Batman villain, which is why he's been adapted so many times and is featured again in Reeves' take. Whether Joker appears in The Batman 2 or another future movie remains to be seen, but having him in the movie immediately becomes one of its biggest talking points. It doesn't overshadow Riddler because he's kept to the shadows and is only given a brief, one-scene introduction that doesn't even name him or show his face properly (as well as Dano's own great performance). The Batman's deleted scene, on the other hand, would've likely shown him more clearly, and since it was Joker and Batman together, would've been one of the biggest, most exciting and meaningful scenes of the entire movie. That's good in isolation, but less so when it detracts from what the Riddler is doing.
The Batman's deleted scene means the movie still sets up the Joker for more and gives him a memorable scene, but doesn't dominate the movie - and indeed, Joker being so hidden makes it more exciting because it's something different and just a tantalizing hint. Even though it would've only been one extra scene, the contents of it - the reveal of Joker's history with Batman, and that he's already been defeated - raise a lot of questions and carry some significant implications that would've hung throughout the rest of the film, never being addressed. It's much cleaner for The Batman to remain more focused on its established threats, especially with so many villains already in the mix, and then move on to the Joker in a future movie if that's what Reeves decides to do.
