Let's see. Goku would be the absolute weakest saiyan. because his mom was apparently weak and his father was an average warrior but a brilliant scientist!. He'll constantly get his ass kicked by just about everyone. Bardock, due to being able to have visions and urging King Vageta to rebel against Freeza, would earn status, so Goku would hang around Prince Vageta a lot and get bullied (Think Deku and Bakugo). Because he's constantly getting his ass kicked he'll eventually become the most powerful saiyan in existence (Because saiyans get a surge in power every time they nearly die), but due to psychological problems, from the bullying and constantly losing, he'll hold himself back whenever he fights... etc etc. I don't really have anything past this. Maybe he crash lands on earth for... reasons. Meets Chi Chi and she gives him the emotional support he needs to overcome some of his issues, go ssj and defeat Vageta. Or something.