Gohan's only achievement is Cell and Vegeta. That's it. He got trashed on Namek, trashed in the Buu Saga beyond a 5 minute fight, trashed in Super.
Gohan is garbage, lets be real, and even with Cell he helped to get 16, Trunks, and Goku all killed. Granted Vegeta didn't help, but Gohan was a bitch during the fight, just like with Super Buu.
Hell even Vegeta, the only thing he did was Great Ape and the spirit bomb reflection, one of which was thanks to Goku and the other he wasn't even conscious for, and Vegeta helped distract Cell at the end, though to be fair on this one, Vegeta is the reason Gohan's arm was broken.
Gohan has always kind of been trash and garbage, as much as I love him and the Cell Saga, he's just a trash character. His real achievement his having Pan and fucking prime teenage Videl.