Gohan Beast's power is incredible and surpasses that of Goku and Vegeta, as stated by series creator Akira Toriyama. Gohan easily defeated Cell Max, a foe that other Z-Fighters struggled against ...

It's really only through the intervention of Krillin, Gohan, and Yajirobe that Vegeta is ultimately defeated. By the time the Spirit Bomb is being called upon, Goku cannot fight for himself anymore.