Son Gohan has always been shown to have incredible potential in the Dragon Ball anime and Manga, but unfortunately, after his greatest victory against Cell, he kind of slacked off a bit and because of that he was surpassed by Goku and Vegeta. Even during the Buu Saga, Gohan was ill-equipped to face off against the power of the Majins rendering the character useless in future arcs.
However, what would have happened if Gohan never slacked off and continued to train even after the demise of Cell. We can hypothetically predict Gohan’s hidden potential by calculating the power boosts he received throughout the events of Dragon Ball Z and Super.
Gohan During The Android Saga
During the Android Saga, Gohan had already started to catch up to the power level of Goku and Vegeta. During his training with Goku in the hyperbolic time chamber, he was able to unlock both Super Saiyan and Grade 4 in just one year. Goku was amazed by his exponential growth and this is the exact reason why Goku chose Gohan to defeat Cell.
According to Vegeta, Saiyan-Human hybrids have greater potential than full Saiyans. This was proved when Gohan advanced to SSJ2 during his fight with Cell, even though Goku, Vegeta and even Trunks had trained much harder. Later on, Vegeta would even go on to admit that Gohan was the strongest Z-fighter and could easily wipe the floor with the rest of them.
Gohan During the Buu Saga
By the time the Buu Saga began, Gohan underwent a huge change both in personality and power level. He was much weaker than the SSJ2 Gohan in Cell Saga and his attitude towards training and fighting meant that Vegeta and Goku were both able to surpass him. Goku had achieved SSJ3 during the seven-year gap landing him leagues ahead of Gohan.
However, during his training with the Supreme Kai, Gohan was once again able to surpass Goku by training only for a few days. Ultimate Gohan or Mystic Gohan, whatever you choose to call it, was the strongest form of Gohan in Dragon Ball Z. In his base form, Gohan was superior to SSJ3 Goku. Just Imagine what Gohan could have achieved if he had proper time to train and better teachers to guide him.
Gohan In Dragon Ball Super
In DBS Gohan had entirely given up on fighting and started focusing more on his role as a father and family man. With Goku and Vegeta unlocking the Super Saiyan God form, Gohan was long forgotten as a viable warrior and fighter. However, Gohan proved everyone wrong once again. Not only did he take part in the Tournament of Power, but he went toe-to-toe against some of the strongest fighters from the Multiverse.
His fight with dyspo shows the pinnacle of Gohans power as he faced off against the man who gave Hit a hard time. Just a few arcs earlier, Hit was the strongest character that Goku had ever faced, and with just a few hours of training, Gohan was able to surpass him and even Golden Frieza.
In Conclusion, there is absolutely no doubt that Gohan has the most potential out of all of the Saiyans in Universe 7 and possibly the whole Multiverse. If Gohan had given proper dedication to his training during the seven-year gap, he could have easily surpassed Goku and Vegeta and even defeated Buu without a fuss.