Though he wouldn't of been able to do it without the other Z fighters' assistance. Piccolo and the others bought Gohan much of the time needed for him to hold Cell off, while Vegeta's attack was enough of a distraction for Gohan to finish him off.
True but Gohan's attack had to be so far above Cell's PL to not only damage him but to take him out completely. Vegeta's Final Flash was able to cut Cell in half iirc yet not enough to kill him. Goku also took out half of Cell with a powerful attack yet it didn't kill him. Cell's own explosion (Which killed Goku) wasn't even enough to take him out.
Cell was distracted but his PL was still crazy high and at half strength Gohan completely obliterated him. Completely destroyed every single cell in his body. At half power.
That makes it pretty clear that Super Duper Cell was still weaker than half of SSJ2 Gohan
It's kinda hard to measure just how much he was above Cell after Cell returned from self-destructing, but being able to disable one of Gohan's arms and thus cutting his strength in half at least says something as far as Cell's power increase, since before he couldn't damage Gohan with even the distructo discs or anything.
He was badly injured because he didn't block the attack he just took it full force to protect Vegeta. The good guys have shown that they can be harmed by vastly inferior attacks if they aren't prepared while the baddies usually mantain their durability at all times. Like when Broly tanked Vegeta's attack while just walking to Goku yet Krillin hurt Goku with a rock while he was resting.
Seeing as how Vegeta still remarked on how much weaker Gohan had gotten and how "soft" he became when going SSJ2 in front of Kibito, it's not a guarantee that he was still above Cell just because he could still access SSJ2. Either way, Dabura pretty much made him look like a complete amateur who hadn't really fought before when he faced him.
I know that there is no guarantee about where his PL actually was compared to his teen self but there was no indecation that he fell to less than half of what he had. And him at half was still superior to Super Duper Cell. Just my opinion.