I totally forgot about GT lol. His character is pretty much set as that because it's so appealing to the Japanese audience, he's like a legit celebrity over there lol.
If you want to see a dumb as fuck character then watch fire force, think he's probably meant to be autistic though so I guess he has an excuse. In one scene he's losing a fight because he can't use his full strength for some reason....he then works out he's holding his sword in the wrong hand, that's some autistic shit right there and not even something Goku would do lol. Animation is amazing though lol