When I was younger I disliked what they did to Gohan. Nowadays I'm thinking it might have been the right decision.
DB is Goku's story, so Gohan should never entirely take over the spotlight for very long.
Gohan also never had the instincts or craving for battle like Goku/Vegeta did; he was always fighting because he had to rather than because he wanted to.
It therefore made sense with his personality, being half-human, and in a time of prolonged peace that he would stop training/fighting and become an intellectual.
Gohan also peaked with his Ultimate Potential/Mystic form, so he's no longer going to be called upon for his latent abilities like in earlier Z. In other words, unless he specifically trains to become stronger, post Z he is pretty much useless for anything beyond Buu level power.
Well, I don't watch Super, so I don't know how they've twisted it now for fan-service, but that is my take.
I see a lot on the internet about fans getting mad over characters not getting prominence anymore. If every character that fans liked remained relevant (pushed by some ridiculous plot device or handwave), the story wouldn't feel as genuine/logical (largely the reason I've been turned off Super). Unlike other series, DB relies heavily on vertical scaling the characters, so it inevitably has to let a lot of characters fall behind the Saiayans.
