This logic makes me shiver with its sheer brilliance.
Here is the logic in a simple way:
-Someone with 3x less the power level can still kill that person. Ie a power level of 10 can kill a power level of 30. This is undeniable and proven. Which makes Brolys power level far beyond 450,000,000. Since SSJ1 Goku is around 150,000,000 officially.
-5 super saiyans combined couldn't kill Broly. Their power level combined was at minimum 750,000,000 or so in the first movie.
-Broly probably got a zenkai, hes a saiyan, so why wouldnt he. He raged out for 7 years. His anger level must have been extreme.
-Broly was not at all powered up or angry in either movie. He was laughing and it was clear his potential was not reached. He still lost because he is an idiot, thats his character, a giant powered up idiot.
Your logic: -3 super saiyan 1s somehow were strong enough to handle him, even after all that happened in the past when Broly was weaker and 5 of them couldnt do it.
gohan never said that?
then how you translate the fact that gohan said when buu was resurrected that he has a change at long as he unlease his full power?
and he was already ssj1 when he made that statement