GT isn't by Toriyama, is it? He just "overlooked" it.
GT simply shows how strong they'd grow if they intensively trained for 5 years.
Furthermore, GT is also the only source where we see their powerlevels after the main story before all the Super bullshit happened.
This is just an assumption. He could have potentially gotten even angrier.
Also, reminder that Goku literally accomplished nothing against Uub beyond postponing.
Uub's potential already started when he reached Kid Buu levels of Ki when he was getting angry.
Goku postponed the battle because he wanted to train Uub, he didn't do it because he couldn't accomplish a thing, lol. He could simply turn into a SSJ and beat Uub with it but Goku wouldn't have fun doing it either.