When The Beyonder has full power, he could easily beat Dr. Manhattan. Everything that Beyonder proved he could accomplish — including destroying all multiverse — supersedes what Dr. Manhattan had even accomplished in DC's Rebirth.
Doctor Manhattan is pretty much the definition of raw power in the DC Universe (even if he's only sort of part of it), and Black Adam stands no chance of beating him.
Eventually, Captain America defeats Kang before Ravonna uses his time crystal to regress him to an infant. In the post-credits, an elderly Kang joins Ravonna, Cosmo the Spacedog, Man-Thing, and the Supreme Intelligence in warning Captain America, Captain Marvel, and Iron Man of a new threat.
Thanos should not be underestimated in any fight, but unless he's wearing the Infinity Gauntlet or has a literal sack full of Cosmic Cubes, he isn't beating Dr. Manhattan. Without the aid of any super powerful objects, or pants for that matter, Dr. Manhattan could easily snap Thanos out of existence.
As long as he had his spear and ravens alongside him, Odin would be able to see all the versions of Dr. Manhattan and battle many of them. Although he could fall in battle, he'd certainly defeat Manhattan as he fell, eventually returning from Hell again good as new.
But what makes Moon Knight so impressive? The comics hold many such pieces of evidence, and one among them was single-handedly beating Kang! How Moon Knight Absolutely Demolished Kang in the Comics? Although it may seem unlikely at first, Moon Knight and Kang the Conqueror go way back.
While Kang almost gets the better of Deadpool, the latter easily takes down the supervillain with a swift kick, something that would play out hilariously in the MCU.
He also ensures that some of the technology Kang will need gets invented (Tony's time travel machine). As he gamed this particular fight over and over, maybe more than 15 million times, He Who Remains chose this specific set of events. He caused Heimdall, Loki, Gamora, Black Widow, and Iron Man to die.
Doctor Manhattan tried to erase Superman from existence yet he kept on coming back. Superman is the centre of all DC and without him nothing would exist. The metaverse forms around Superman.
Dr. Manhattan is very powerful, but not on the same level with the White Phoenix, which is the most powerful version of Jean Grey and the Phoenix Force. They finally became one entity, where before Jean was only a host. She literally becomes a god.
Again, while Doctor Manhattan has a wholesale of other superpowers when it comes to proper fighting technique, Ultra Instinct Goku beats him in a heartbeat.
Kara Zor-El has the same basic power set as her cousin, Superman, making her yet another DC superhero capable of defeating Darkseid. Like Superman, Supergirl has also beaten Darkseid in the comics and their adaptations, with one notable example being the animated movie Superman/Batman: Apocalypse.
However, the Hulk was able to interfere, stopping Kang and helping the Allies win the war. This kind of conflict avoidance felt out of character for the warlike and paradox-averse Kang anyway, so it's probably best that he abandoned his plans to alter the Avengers' history.
Kang is stronger then Galactus! Kang is a threat for the entire multiverse (so also What If...?, Raimi and Webb trilogies, Fox X-Men Universe), has millions of Variants + the entire TVA can travel through the multiverse and through time!
Galactus was killed by Thor during the "Herald of Thunder" story arc in Thor (vol. 6) #1–6 (March–August 2020), and reappeared after a two-year hiatus in Fantastic Four (vol. 6) #45 (July 2022)—the final issue of the event "Reckoning War"—where Galactus is resurrected by his former heralds.
Spider-Man and Kang have fought several times, and the Wall-Crawler was always able to beat the Conqueror. Kang underestimated Spider-Man, something that many powerful villains have done, and he paid for it. In one of Kang's first attacks, he created a Spider-Man robot to take out the Avengers.
Even though the 616-universe's variant of Thor might harbor enough power to take on Kang the Conqueror by himself, Hemsworth's comments about potentially retiring the role suggest that Kang would, in fact, overpower the Asgardian.
Kang the Conqueror may be the strongest villain in the MCU yet. But one Eternal can stop him if he can survive long enough to face him. Kang's growing presence in the Marvel Cinematic Universe has inadvertently disadvantaged many of its heroes before they've even met him.
Unfortunately, as formidable as the Hulk has been in all his incarnations, brute force may not be as effective against Dr. Manhattan as his other adversaries. Manhattan could conceivably split Banner from the Hulk as Onslaught did in the '90s, or disintegrate the Hulk from existence altogether.
We've only seen a brief glimpse of them but the Celestials are also probably more powerful than Dr. Manhattan. The Dread Dormammu could win against Dr. Manhattan.
In short, in a straight-up battle, Dr. Manhattan could easily destroy Superman. All he would have to do is disintegrate him and no matter how powerful Superman might be compared to other beings, Dr. Manhattan is simply too powerful.
