Can I answer both? Ima answer both, because I believe both have problems.
So, to the "SS believers", I have this question:
- Why didn't Gohan use Super Saiyan 2 while the whole universe was at risk when Majin Boo was about to be revived, and also revived later? He was even trying to power up even more by drawing power from his anger. Don't forget that he could easily transform into one against Kibito, so he hasn't lost the ability.
I have a hard time answering this one. I really, really don't buy that he couldn't transform, or that he couldn't find an opportunity to transform because it's simply not that hard. At the Budokai, he's calm, and his transformation seemingly takes no time at all - once he actually decides to transform, it happens. The crowd complaining and all of that only happened while he was still uncertain on whether he should transform at all, not while he was actually trying. Plus Dabra blasted him into the water, and sat around mocking him at times. It's clear that Dabra was not constantly putting pressure on him like what would have had to happen for Gohan to have no opportunity to transform. This has always been an extremely unsatisfying explanation for me. The only worse explanation is "he can't go Super Saiyan 2 any more, except for when he could 10 minutes ago" because that's something the story really should have explained if that was meant to be the case.
The only other explanation I can think of would take a certain interpretation of this quote:
Chapter: 458 (DBZ 264), P6.1-2
Context: after Majin Boo quickly reaches full power
Kaioshin: “Th-that’s impossible…Wh-why has Goku’s damage energy [filled it up] already…!?”
Gohan: “…I-I know…! Father is fighting at a level that has further surpassed Super Saiyan…Vegeta probably is too…If two incredible powers like that clash, th-the damage is astounding too…!
...to mean that Gohan deliberately avoided using Super Saiyan 2 to avoid giving Boo more energy, since Super Saiyan 2 uses more energy than Super Saiyan 1. If Dabra wasn't capable of extracting energy than Super Saiyan 1 Gohan, it might be best to stick to that and try to turn the fight around gradually, instead of using Super Saiyan 2 and immediately gaining the upper hand at the cost of giving energy to Boo from using the form. I had previously thought this might be the case, but seeing the quote with Herms' more accurate translation, it definitely sounds more like Gohan's just saying the stronger both fighters are the more energy is released from the damage. It could still be the case that the energy consumed by transformations fuels Boo, but the quote doesn't appear to support that. It also wouldn't explain why Gohan didn't use it against Boo.
Another reason he didn't use it against Dabra is maybe he just wanted to conserve his energy, but I'm not sure why that would be the case. They were told that Dabra was basically the final boss, so there's no reason to hold out. It's possible Gohan felt that it wasn't power he lacked, and that Super Saiyan 2 wouldn't help offset his own rustiness - maybe it was that he knew he could win as it was, if he managed to adjust to to the fight and Dabra's tricks. Or maybe Kibito just fucked up and didn't actually restore all his power, so he didn't have enough to transform.
Against Boo, it's harder. Perhaps he was able to produce a Kamehameha at its strongest without turning Super Saiyan 2? Who knows how it works, maybe putting everything into a Kamehameha takes the energy he'd use for Super Saiyan 2 as well. After he used the Kamehameha, he could just be too exhausted to maintain anything but the regular Super Saiyan state.
To the "SS2 believers", I have this question:
- Why doesn't Gohan have the SS2 aura? SS2 always granted to the user an intense aura with sparks, yet Gohan's aura in identical to that of normal SS. The excuse that he got weaker doesn't work, because he displayed the SS2 aura with sparks just fine against Kibito.
I don't believe SS2 necessarily does have its own aura. The only thing that says this is the GT Perfect Files (which make a mistake in the same sentence they say this, and we're not using anything but the manga) and so there is only interpretations of the arc. It could just be that sparks are entirely stylistic, and represent power - Gohan was previously shown with sparks when he was the strongest character we knew of, and it wasn't yet revealed how much weaker he'd become.
And the weaker = no sparks SS2 argument can work if you assume Kibito didn't restore his energy, or he'd already lost some from fighting Dabra. I don't think he would have lost enough to drop out of Super Saiyan 2, but I could see the sparks going away if he's only able to produce them at close to 100% because he's weakened.
Besides, when Vegeta fights Pure Boo, he only has sparks in one panel after Pure Boo hits him. Compared to sixteen panels
of him lacking sparks. So I don't make too big a deal out of missing sparks.