>>533518094
SS2 isn't treated as that massive of a boost. Piccolo comments that Goku and Vegeta would never be able to defeat Buu with SS2, no matter how many there were. In BoG Beerus doesn't really care about it too, it's only when Goku used SS3 that Beerus reacted like the fight would be fun. I think this is why SS3 has such a big jump, it could easily be 2x SS2, but the power it's implied to have is meant to be overwhelming.

>>533521502
I don't know about that, Cell was holding back the whole time, and Goku talked like Gohan only stood a chance if he unlocked his potential.

>>533521935
Goku also says that Gohan isn't unleashing his full power because he's afraid of destroying Earth. Also while the series itself hasn't talked about it, Toriyama mentioned in interviews that things like confidence and courage make you stronger, and letting yourself lose control of your emotions will mess up your ki control (or something among those lines), and I feel that applies here. Gohan screwed up, lost confidence, he now feels weaker because of it. We also had Nappa throwing a fit when fighting Goku and being overwhelmed, but when Vegeta ordered him to calm down, Nappa fought Goku better to the point Goku himself and Vegeta were thinking the battle would take a long time to end.

In short, emotions affect your ki. I don't know why the franchise never explained this at any point, having Korin or Popo explain that to Goku would make sense...