FunkDoc1112
Heavily Armed
First up, he wasn't "powering up..." he was attempting to power up but he alreayd knew it wasn't gonna work. He was visibly struggling against Cell and his last few attacks were shaky and desperate, the type of shyt Vegeta does when shyt gets tough. He was confident despite Cell's clear superiroty because he knew Gohan would get it done. He fought Cell so Gohan could see how he fought, which Piccolo correctly deduced.wow, the age old topic of whether goku could have beaten cell or not is back i see....well, the correct answer is: yes...goku could have beaten cell....the manga shows this, and the tv show, which followed the manga closely, showed this....just look at the manga/show again...when he starts powering up and goes past ss1, shaking everything/scaring everyone with his power, he stops, smiles, and says lets go to gohan....he never finishes powering up all the way, but it's hinted at that he could reach ss2.....that's the reason he knew about ss2 in the first place, and that gohan could reach it.....now, the reason he didnt go all the way nor beat cell was cause the creator didnt want him to...he's said this in interviews before: he wanted gohan to be the face of z going forward after the cell saga, that's why he had gohan do it...but fans complained that they wanted goku to be the face of z, changing his plans.....hence the reason goku is the one always saving the day after the cell saga, the reason gohan stopped training/getting stronger, etc....z was supposed to be the gohan story, the same way dragon ball was the goku story...
Second of all, that whole shyt about Toriyama getting pressured by fans to bring Goku back is false. it's a rumor that's been around so long people think it's true even though he's never actually said it, just like the "DBZ was supposed to end at the Frieza saga" myth. What he DID say was that he decided that ultimately, Gohan wasn't suited as the main character, and so he chose to bring Goku back. Not the fans.
As for the USSJ stuff...I think in theory, USSSJ is almost, if not just as powerful as SSJ2...but it's just a raw transformation with drawbacks, essentially flexing your muscles. Gohan was the only one who figured out how to actually ascend and reach that power without the loss of speed and massive energy strain.