Yeah, I figured that. think about it. In the first movie, Gohan never transformed to a SSJ2 because he didn't know he could. If he did know, I'm pretty sure he would have considering how much Broly was overpowering Goku and the others. And in the second movie he was having trouble against him as well because he had "gotten soft in the times of peace" according to Vegeta when they were in the ship where Majan Buu was.
Yes you are so right it really sucks that gohan did not trian in the times of peace he would have been a lot stronger maybe even stronger than goku I also think that he would have defeted buu no problem