Maybe controversial, but perhaps they should have made SS3 Goku, SS3 Gotenks, Ult. Gohan, Super Buu & Kid Buu relatively within same ballpark of level. Then bringing Gotenks & Gohan to fight against Kid Buu might not have been a stomp.
If Goku winning isn't unfair, maybe Gohan & Gotenks could have faired bit worse due less focus on training, which is a thing now thanks to Super and Roshi performing well with that logic. Add giving Kid Buu regen that would force them to use a Spirit Bomb to guarantee the win.
I don't really mind Goku being the MC of Dragon Ball. I don't think changing it is necessarily required. It definitely felt like when they entered Babidi's ship that Goku & Vegeta stole focus from Gohan. That was probably when shift from Gohan as MC changed, or at least started.