Here we go.
People say goku is stupid... he isn't stupid, he's just innocent. He never had formal schooling or any stuff like that, but he's VERY well trained. Sometimes he's too dumb to put 2 and 2 together but that doesn't mean he lacks in combat strategy. He in fact excels in it. If you look at dragonball, which made skill and technique more apparent rather than sheer "power level," you see that goku was pretty brilliant.
Vegeta didn't beat Goku in the Majin SSJ2 fight. Were you even watching? It was totally even, until Vegeta goes "Hey let's go fight Buu together" and Goku goes "GREAT!" and turns to get a sensu bean, and while he isn't looking, Vegeta bashes him. You call that a victory? That's just a dirt cheap shot, that has nothing to do with power.