Has Dragon Ball made Goku too powerful to stay on Earth? It's a question that's certainly being raised by the current Dragon Ball Super storyline, which has pushed Goku to finally master his latest transformation, Ultra Instinct. Goku first tapped into Ultra Instinct during the Tournament of Power arc, in order to save his universe from being erased from existence. However that milestone was a fluke, and since the ToP, Goku hasn't been able to achieve it again... until now. In Dragon Ball Super manga chapter 64, Goku is able to finally reach Perfected Ultra Instinct, and it's clear that the power is something that Earth cannot handle!
Warning: Dragon Ball Super Manga Chapter 64 SPOILERS Follow!
In the latest Dragon Ball Super manga, Goku has been pushed to the emotional brink by the death of his mentor, Merus. The angel/Galactic Patrol agent violated Angelic Law to help Earth stand against new villain Moro, and was erased from existence as a consequence. Goku is left feeling that ol' Saiyan rage - but Ultra Instinct is not at all the same as when Goku first achieved Super Saiyan against Freeza. Ultra Instinct requires a fighter to rise above emotion in battle, in order to achieve the perfect serenity between spirit and body that allows for a mode of fighting that's faster than conscious thought.
The scene of Goku finally being able to control his Ultra Instinct transformation is epic - but not as epic as when Ultra Instinct Goku actually fights Moro! The formerly unstoppable villain is no match at all for Ultra Instinct, and Goku quickly outmatches him in every way: offense, defense, and energy manipulation. When Moro flies into a rage at being beaten, he comes at Goku full-force, only to put down for good by Goku's finishing move. In fact, Goku uses an Ultra Instinct version of his Super Dragon Punch to levitate Moro into the air, and deliver a rising uppercut that's so powerful, the shockwaves reverberate across the entire Earth, and into space.
Ultra Instinct is a divine power, which Goku was only able to learn by studying with angels like Whis and Merus, who use the technique in battle. Both angels were prohibited from fully manifesting Ultra Instinct and fighting with it on the mortal plane, as doing so would be a display of power that violates Angelic Law. That rule is important to note - as are the reactions that various divine figures (angels, Kais, Gods of Destruction, and even divine leaders like Grand Priest and Grand Zeno) have had to a Saiyan mortal achieving Ultra Instinct. Goku may not just be too powerful to fight on Earth any longer - he may too powerful for the gods to keep him on the mortal plane, at all.
Dragon Ball Super fans have long speculated that the series was building to a finale in which Goku has to evolve or graduate to the divine level - while leaving the rest of the Z-Fighters to their own series of adventures. It's the kind of big change Dragon Ball has been pushing toward, and it's getting harder and harder to see how it can avoid that crossroads.