Gohan trained with Piccolo forever while Goku was dead, he underwent an emotional journey, and had the deepest character development. He was a pacifist who was forced into fighting just to protect his friends. He was kind to everyone, he was the first person to be kind to Piccolo and not treat him like a monster, so Piccolo risked his life for Gohan. Gohan didn't want to see people like his dad who just try to resolve things with violence. He was pushed around by ChiChi to study books, and he didn't complain to either ChiChi or his dad, who both just forced him around, because he is above that, he realized that enjoying life is more important than trying to control it. Gohan trained as hard as possible with Piccolo, and with every enemy he was forced to fight and gained experience fighting Radditz, Vegeta, Freeza, and extremely well versed fighters before he was even 10 years old. He is naturally the best saiyan because a super saiyan is defined by the light hearted traits that Gohan possess, allowing him to surpass Goku when the perfect enemy arrives, and through battle experience, intensive training, and inner peace he became the strongest single character in Dragon Ball. But ironically he doesn't care about the powerlevel game like the rest of the idiots he lives with. He just wants everyone to be safe, even his enemies he grants mercy until there is absolutely no other option. Gohan avoids fighting, but is still the best fighter ever.