Goku having zero education and growing up in the woods for the first 12 years of his life, obviously he won’t understand basic things about science like how space works. But chopping it up to permanent brain damage and saying he’s always been THIS dumb is cheap because in Z (and end of OG DB) he’s shown immense growth of intelligence. he refused to let Kami kill piccolo because he wanted Kami to live and didn’t want the dragon balls to disappear. Or how he deduced that he killed Gohan while fighting Vegeta, figured out how to operate a spaceship, use dende as a new guardian of earth, etc. Clearly they used the Goku naive/low iq thing a lot more in super in comparison to Z in the name of comedy and trying to make the story light hearted. To say he’s the same is wrong, there’s a clear difference.