I also think that Broli's power is amazing thing indeed....becuase even without training he was stronger than at least a normal super sayian, a good bit anyway. But he does have a limit to his power.
Think of Broli as a super gifted person...like a kid with a lot of natural ability. He was born with his crazy power, it wasnt given to him. But had he recived correct training, his power would have far exceed any DBZ fighters.
Another thing is, during the first Broly movie, Broly was at a comparable size to Trunks in the cell saga when he went Ultra Super Saiyan.
http://upload.wikimedia.org/wikipedi...per_Saiyan.jpg
The only thing is that Broly didnt have the speed disadvantage as Trunks did, he was just as big and maybe more powerful, but was still very fast. Maybe pushing him to the power of a super sayian 2.