Warning! Spoilers ahead for Dragon Ball Super Chapter 82!
Aside from the obvious fact that anyone defeating an enemy except Goku would have broken a stagnant trope, the current fight between Goku and Gas would have been much more interesting if Buu had defeated the villain Moro from Dragon Ball Super's previous arc as was originally intended.
In chapter 82 of Dragon Ball Super's latest installment, Goku enacts a rather ingenious strategy using Instant Transmission to trap Gas on a faraway planet, believing that the villain wouldn't be able to follow him back. One of the places he leads Gas to is the Galactic Prison where the two interact with a few minor characters from the last arc—the Galactic Patrol Prisoner Saga. Although a pleasant nod to older enemies, this moment could have been much more ominous if Buu had successfully sealed Moro instead of Goku destroying him.
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During the Galactic Patrol Prisoner Saga, Goku and his friends' original strategy against the rampaging Moro was to leverage the power of a god whom Buu devoured when he was still a villain. Long ago before Goku was even born, Moro was terrorizing the universe, and out of the many heroes who valiantly tried to stop the dastardly villain, only Grand Supreme Kai could defeat him by sealing Moro—who was then imprisoned at the Galactic Prison. Since Buu later devoured the Grand Supreme Kai when the Majin was still evil, it was theorized in the present day that Buu could leverage the Grand Supreme Kai's power to seal Moro away once more. But it unfortunately became apparent as Buu began fighting Moro that he didn't possess that sealing capability since it had transferred over to Evil
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