Kento is acting stupid here, and he's arguing like a noob.
Galan is right. Gohan was SSJ2 against Dabura, which is what embarrassed Vegeta and Goku. Either of them probably could've handled Dabura in SSJ1. Galan has already argued this to the point where it's like beating a dead horse. Vegeta though to himself, "Kakarot has ascended past SSJ too", which means that he was referring to himself having ascended past SSJ in the first place. He wasn't referring to Gohan, because they already all knew that he had SSJ2, this was old news.
Also, Majin Vegeta had lightning. Dabura didn't have lightning, so the lightning was caused by Vegeta being SSJ2. IIRC, Majin wasn't even a buff, it just made him heartless and made it easier for him to fight Goku with the intent to kill.