The intelligence nerf doesn't change much, seeing as how GT Goku was as idiotic as his kid self anyway. However, nerfing his power means he likely wouldn't be part of the group heading into space so either Piccolo or Vegeta would go to provide Trunks the additional power, most likely Vegeta since Piccolo wasn't around and Vegeta's only real reason for not going in GT may have been due to him wanting to be a good father for Bra.
With Vegeta as the leader, the events of the main plot likely go far more efficiently than in the main timeline due to not having Goku acting like an idiot or wasting time holding back against what was overall fodder. Baby would still likely find a way to retreat and get to Earth, though without being able to possess Vegeta, Baby's best alternative is to stay in Gohan's body. The timeline goes two ways depending on whether or not Baby draws out enough power from Gohan to enter a form similar to when he possessed Vegeta.
1. He fails due to Gohan only needing to go SSJ against Goten. When Vegeta returns to find out what happened to Earth, he kills Gohan-Baby and restore the Earth to it's natural state. As for Goku, he could be easily restored to his adult form by transporting the Ultimate Dragon Balls to a spaceship and making the wish there, thus avoiding the damage they'd have on the planet they were used on. However, this would prove meaningless by the Super #17 Arc, where Piccolo not being in Hell would mean Goku is trapped there permanently and the lack of SS4 means everyone is killed by Super #17.
2. Baby is able to power up Gohan's body in a similar manner to as he did Vegeta's. The Baby Arc's structure remains primarily the same beyond Gohan being Baby's main host and Vegeta taking Goku's role in achieving SS4. Super #17 Arc remains mostly the same. Whether it's Goku or Vegeta who's transported to Hell makes no difference, considering the overall outcome is still #17's defeat. Only thing that may change is Super #17 being killed far quicker if Goku is the one trapped due to SS4 Vegeta not needing to use Ki attacks and just dismantling him with a few physical strikes.
As for the Evil Dragon Arc, no SS4 fusion means everyone is killed by Yi Xing Long. Even if Goku uses the Bruits Wave Machine to go SS4, the fusion would be so much weaker they'd still lose.
Looks like nothing can go right in the :toei universe without

.