You know what?, this shit should make Goku outright Above Average at least, even Gifted with the bolded part, because he literally need to understand some of Tuffle's biological physiology to deduce that weakness.
Also you forgot that he decided to wait for Baby spaceship is in the right position to fire a Kamehameha to push him to the sun to "negate" his regeneration
Personally this moment feels like PIS for Baby. The whole reason this works is because when Vegeta grew, “Baby grew too.” So when Vegeta shrinks to normal, Baby is too big to fit in Vegeta’s body.
Which on the surface seems okay/sensible, but doesn’t make tangible sense when you stop and think for like 10 seconds.
1) Baby has made himself significantly larger than his targets to possess them before. Most clearly with Gohan, where before he possessed him he turned himself into the giant form of his head and overlapped them. This never limited him before.
2) Baby possessed Meta Rildo and had him merge with the planet, which is Rildo’s
real body. In order for Baby to do this, he must have made his mass
planetary to exert the control we visibly see him have over Rildo and the planet. This did not affect him whatsoever for his later possessions.
3) Baby can shapeshift. Like
incredibly well. Like, he’s shrunk himself to fit in cuts. Even though his mass is
significantly larger. (Goten fight, Vegeta). In fact, Baby himself literally escapes Vegeta’s body by
shrinking into a rock’s size, and hopping away.
By all accounts Baby
should’ve been fine. The fact Goku doing this worked is plot at its finest and probably should be considered an outlier on the negative end on Baby’s profile. Which is why I only give it passing mention.
EDIT: My personal Headcanon I don’t use for the profile is that it’s not that Baby couldn’t make himself smaller, but that doing so simply would be
too slow to save himself before he’s compressed and killed by Vegeta’s body. Essentially, Vegeta’s shrinking
too fast to compensate for.