Gohan needed to take him down and grow to be a little cynical.
Agreed though. Cannot believe they did Gohan like that. Spend almost the entire series building this kid up, showing the hardship he's overcome, the pain he's had to endure, the enemies he took down like Cell. But highlighting very much so he couldn't have taken down Cell without help from his dad and everyone else. When things were at their worst, he needed that mental pep talk from his daddy to persevere and dig deep. He wasn't ready to be the Hero of the planet. And that's what the Buu saga was about before the stupid ending.
A good amount of the saga built up to it which made it even more lame when he didn't get to take down Buu.
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The Great Saiyama arc was pretty in your face about it. He granted himself the role, and played it up hard striving for glory and attention. 2 character flaws Goku would
never
in a million years have. Which set the foundation for his character arc. To grow more like his father.
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The whole season was also self-aware about how ridiculous super saiyan transformations can get. Little kids fuse. There's some electricity. Goku grows longer hair. The show even pokes fun of that. And then here comes Gohan's "transformation". He finally gets his training with Old Kai, and he unlocks his latent power. We get to see him transform. And he looks exactly the same. He looks like a human. And that's what his latent power unlocked, the power that rest within his human blood.
Gohan gets this absolutely badass entrance. Piccolo even mistakes him for Goku
https://www.youtube.com/watch?v=OSz2ZJ8RSeY
He's cocky and arrogant as ever showing he's got some much needed learning to do. He gets brutally beat the fuck down both physically and mentally. Buu wages some absolutely filthy psychological warfare against Gohan. Beaten the fuck down, ridiculed about how weak you are without your father, and manipulating your mentor's thoughts against you. Gohan was in a seriously fucked up position. The stakes were higher than any other fight in the series, more than any of Goku's. And this could have been a turning point for his character. There literally wasn't a soul alive to help him at this point. It was on him to grow right here and find a way to win and save the world.
It would have been a truly fantastic ending to the series.