What if: Goku and Gohan used all the days training in HTC

[Bussani]

Sorry that I don't have scans, you guys will just have to take my word on that, but I'm positive that other people with the Viz manga could verify me.

I can, but their translation isn't perfect in this case. Here's a more accurate translation, which has an interesting note on the subject.

Chapter: 407 (DBZ 213), P5.3
Context: as the Cell Juniors beat everyone up
Cell (to Gohan): “If you don’t show your true worth soon, things will go past the point of no return. Look closely. Vegeta or Trunks are barely fighting evenly…Even Son Goku is in trouble, having lost his stamina…”
Note: Cell says that “Vegeta ya Trunks” are fighting evenly; ya is a non-exhaustive word for ‘and’, meaning the things listed aren’t necessarily the only things there are to list. In other words, Cell’s line doesn’t necessarily mean that nobody but Trunks or Vegeta are fighting evenly, just that they’re the first examples to come to mind

[Saiga]

They didn't master the SSJ transformation like Goku and Gohan did.

They very well could have. They didn't used the grades at the Cell Games, just basic Super Saiyan.

[Bussani]

Vegeta and Trunks also had the same type of aura as Goku and Gohan while fighting the Cell Juniors, for whatever that's worth.

[Rostir]

They didn't master the SSJ transformation like Goku and Gohan did.

They very well could have. They didn't used the grades at the Cell Games, just basic Super Saiyan.

I agree.