Warning: This article contains spoilers for The Batman.
With The Batman, DC opened with a good grip on the box office and has been met with stellar reviews, seemingly matching the level of success MCU projects have received, but its Joker setup and a likely The Batman 2 could risk it repeating an MCU mistake. The Batman is the latest in a long line of Batman reboots, now placing Robert Pattinson at the helm after Ben Affleck's canceled Batman movie as Affleck and Michael Keaton have uncertain futures in the role for the DCEU around The Flash (2023). The journey to Matt Reeves' The Batman has been rocky, and the risk of it repeating an MCU mistake might doom the franchise's future.
The Batman takes on the mystery noir genre, distinctly separating it from typical superhero movies which have seen a resurgence with the MCU. The MCU clearly has a winning formula which includes a mixture of comedy, good action, likable characters, and an open multiverse. Now other markets are trying to emulate and cash in on this model. The Batman's distinctive move away from this formula is a brave act in the film industry, but The Batman 2 might collapse this wing of the franchise's own legacy.
The mistake would be to give The Batman a sequel, which could contribute to the over-saturation of comic book movies and ruin what makes the film so different. It's definitely teased for a sequel; the Riddler's familiar Arkham neighbor in the ominous post-credits scene and the release of the Joker/Batman cut scene. Whilst the MCU is hugely popular and successful, it has no doubt played a part in the overextension of superhero films, endless sequels, and cinematic universes. Giving The Batman a sequel with an overdone villain would play into everything it strove to be different from, thus it could be a huge mistake.
The Batman is a complete change of pace from the formula of comic book movies; it's serious, grounded in realism, with just a touch of comedy that doesn't take away from the overall tone of the film. The MCU can face criticism sometimes for its overly jokey scripts and a lack of sincerity, but The Batman is different from this and as a result, its atmosphere is perfect. It's also a lengthy film, coming in at around 3 hours long, which means that it was able to explore each main character in a good amount of detail. Catwoman and Batman had good arcs, Bruce and Alfred's relationship was concluded nicely, and Batman had a well-established partnership with Gordon. The film doesn't leave any crucial loose ends to tie up, and its conclusion works well as a stand-alone movie. Even the Joker tease isn't something that warrants a sequel. There have now been 4 live-action Joker's in the past 15 years and the character is well-known enough. It would be more effective (and unheard of nowadays,) to leave The Batman as a lone movie, rather than potentially cheapening it with The Batman 2 featuring a villain that has been done to death.
Though Barry Keoghan's Joker does look interesting, the character is clouded by how many times he's been brought to the screen in recent times. The MCU has normalized sequels, prequels, and extensive universes so much that it is expected of every film, regardless of whether it's a comic book story or not (the MonsterVerse, for example). The Batman breaks the norm by giving audiences a whole film with well-concluded arcs, and its ability to do so is a testament to its integrity that would be diminished by making The Batman 2.