We know he can't be that weak compared to Goku. Goku was severely weakened by the time he filled up the Buu meter. This confirms Gohan is at least somewhat relative to Goku.
Well, he can't be that weak, but he was way weaker regardless. Vegeta stated Gohan was far, far better as a kid and Gohan was above kid Gohan. That could allow for a 1.5x gap or so between SSJ2 teen Gohan and SSJ2 Goku. If Goku is way stronger, then his damage will amount way bigger energy for Boo. Gohan also had all his power drawn out and contributed to roughly the same amount of energy that a damaged, but still strong enough to keep himself in SSJ2, Goku did... That also shows a big difference. Besides, the clash between Goku and Vegeta led to more damage in general... Gohan wasn't that damage by Dabura, Goku was breathing heavily, with his face bloodied, clothes ripped... It was a more intense altercation, whereas Dabura didn't deal the same damage to Gohan. Weirdly though as I'd argue Dabra should be slightly stronger than Gohan, but it seems the damage was just not that substantial.
I think it took the pointer from, like, maybe ~45% to ~55% ? I don't think it's farfetched to SSJ2 Gohan to have contributed to a 10% add when being barely damaged, or at least, not noticeably damaged, when his entire SSJ2 led to 45% or so.
CGs
Goku
SSJ : 75
Gohan
SSJ : 90
SSJ2 (rage boost) : 320
-- 4x multiplier (while normally, it's a 3x multiplier for everyone else, 3.2x more precisely because that's the number that worked fuck u lulz)
Boo saga
SSJ Gohan : 75
-- SSJ2 : 240
-- little damaged vs Dabra
SSJ Goku : 125
-- SSJ2 : 400
Energy to revive Boo : 530
Post Gohan : 240
--- Dabura's damage : 280
--- Goku's damage : 530
SSJ2 weakened Goku : 150
And honestly though, Gohan getting the pointer from ~ 45% to ~55% would still not fit that much... Since Gohan would be then too weak to compete vs Dabra. It'd be better going from 48% to 52%. Still, moving a 5% in that scale would be like a 27 power loss. If Gohan was a 240, then a 27 power loss would still suck... Maybe it should be even lower lol. But if he were SSJ, then a 27 would take him to like 60% of his full power.
Idk tho probably overthinking