As a fan of JoJo's Bizarre Adventure, I have zero issues with changing the main character of the story part-way through. Hell, do it 9 times for all care, GoGo's Dragon Ball Adventure.
I know JoJo is specifically set-up for multiple protagonists but look at Hunter x Hunter. Both Gon & Killua basically haven't been in the series for the last 50 chapters, and I know in the fantasy land where Hunter x Hunter gets new chapters, they'd eventually return to the spotlight, I'm just saying Gohan shouldn't take over because it's Goku's story, doesn't work for me.
I mean, every since Gohan's been introduced, the story's been building up to his moment against Cell, and we spend a lot of time with him. I honestly wouldn't be surprised if from Raditz's to the end of Cell, we spent more time with Gohan than we did Goku, since Goku mostly only shows up during that period to fight. The series was definitely building up to Gohan taking over the leading role, and by the end of the Cell Saga, Gohan was even more popular than Goku (based on the Japanese popularity poll at that time). That gives enough reason to allow for Gohan to take over as the lead, as the Gohan experiment was demonstrably a success with the readers.
All that said, I'm actually fine with Goku resuming main character role and think it's perfectly in-character for Gohan not to. I wish Buu did a little more with him than they did but ultimately, I love how the Buu Saga ends so I wouldn't change that and am even glad Goku took the mantle back. I just don't find the "It's Goku story so he shouldn't" to be a very a compelling argument.