Of course there are indications that they weren't. Vegeta can punch people through mountains, yet he just punched Trunks in the nose. And no, they weren't using full effort.
He hit Trunks with a quick reactive punch. Full force hits don't always have to launch someone through a mountain, have you even read the manga? Yes, they were using full effort, nothing indicates they weren't. Gohan was even sweating, and Vegeta felt so pressured by the assault that he had to hit Trunks to make him stop. You're just trying to make stuff up to nerf the kids.
Shock doesn't always mean someone is stronger. It just means stronger than expected. You're deductive reasoning is flawed. Piccolo knows the potential Goten and Trunks has, but that's what they had then - potential. In time, Piccolo was sure they could outpace him.
No time, Buu is right there. Also, he already knows the kids are waaaaaay strong for their age- he sensed their ki output at the Budokai- yet their full power still makes him damn near crap himself. Mysteriously Goku, who is stronger than them and Piccolo, isn't intimidated.
Yes, around that power. Goku and Gohan don't even have a right-before-Cell-Games power, they just have their Android-19-and-20 power and their Cell Games power, and their android-19-and-20 power wasn't the one being used in movie 8 for sure. As for Trunks and Vegeta, they have a right-before-Cell-games power and a Cell Games power, but their power didn't drastically change from one moment to the other, it just increased somewhat and they started to use regular SSJ instead of the grades.
Goku has a unique design for his resting state. That's the one that was used here. Not his full power state.
It increased MASSIVELY, actually.
SSG2 Vegeta gets tanked by Initial Perfect Cell, then curbstomped.
SSG3 Trunks is stated to far surpass Initial Perfect Cell.
Everyone senses HALF of Goku's power and is awed by it, even though they all sensed SSG3 Trunks. Vegeta states that half of Goku's power is beyond him.
Vegeta and Trunks train again. From this, Vegeta is sure he's made such big gains that he totally outstrips 50% Goku and can kick Initial Perfect Cell's ass.
Goku and Cell power up, Vegeta moans about how he's been surpassed again.
Hell, LSS Broly only has to be as strong as Initial Perfect Cell to do what he did.
You claim that their power in movie 8 has to be based off the power of Grades Trunks and Vegeta and Goku's and Gohan's power adjusted accordingly, when it makes just as much sense to have their power be based off Goku and Gohan's power in the Cell games and the others adjusted accordingly.
I'm not saying it HAS to be based on anything, I'm saying that no, M8 Broly doesn't look stronger than M11 Broly unless you think they're at their Cell Games levels. Which nothing indicates and some things contradict.
Actually, that method would make less sense. It'd be basing everything around SS Gohan's design (even though he's the weakest in the movie yet by far the strongest at the Cell Games) instead of the other three. Vegeta still uses SSG2, he clearly has not mastered Super Saiyan.
And SSJ Gohan fought terribly agaisnt the same Cell that Goku had fought, even if he was stronger than Goku, because he wasn't tapping into his rage. I have no trouble sseing the same scenario for Gohan in movie 8.
No, he wasn't. He was dodging and blocking Cell effortlessly and floored him with one kick. Sometimes he basically let Cell hit him, but it did absolutely no damage. He didn't lose control of the situation until Cell powered up, using all of his true speed.
Also, melting power..? It's really simple: Bio-Broly appears to be more fragile than Broly since he couldn't protect himself from the goo while Broly protected himself from the lava and all others attacks except the finishing ones. You can say "we don't know!!" and you are right, but the only things that we have to go on point in that direction and that's all I'm stating.
That's assuming the goo is weaker than lava. Which is again completely baseless.
Actually, we have a lot more to go on, like Vegeta being Grade II in M8.