An amped ki attack? It was a suppressed ki attack. Trunks specifically didn't attack at full force with it.
Accurately portraying gaps for what they are is what Toriyama is good at. He definitely wouldn't forget about that here.
That tows the line about Super Boo and stuff, but if it's true, then what is the famous sparring panel meant to convey?
There are only a few puzzle pieces needed to confirm that the sparring scene is indeed an accurate portrayal of Goten's power as being somewhat competitive with Gohan.
Chapter: 377 (DBZ 183), P8.3-5
Context: as Goku and Gohan start training in the Room of Spirit and Time
Gohan: “Dad, am I going to get in the way of your training?”
Goku: “At first,
yeah. But once you’re able to become a Super Saiyan, you’ll really come in handy as a training partner, Gohan. That’s my ideal, anyway. Obviously I intend to obtain power surpassing Super Saiyan. I want to be stronger than anyone, after all. But Gohan, I intend for you to even further surpass me.”
Sparring with a much weaker partner holds you back.
Okay, well maybe Gohan can still gain benefit, sweat and get a good workout even if he's not really being challenged?
Here we see that exact situation. Here Trunks, is obviously the weaker of the two, as he's sweating bullets and breathing heavily. Likewise, Gohan, while he appears to have a single bead of sweat on his face is smiling and looks totally relaxed. This is what happens when two disparate powers spar. Gohan is barely gaining any benefit; it's all for Trunks, and his effort reflects that.
So both a statement, and a demonstration of it in action. I think we can safely classify the scene as not falling into that same category.
Besides, Trunks being able to hit Vegeta and his ability to send Boo flying also suggest a high level of power. Oh, and Piccolo's reaction to them powering up, along with his statement that they're the last hope before fusion is mentioned.
