Welcome to the forums.

Beatrix is very powerful. She was the most famous and feared person in the world and could win of entire armies alone(if i remember well), but i agree with you, the heros should have won in the last battle against her.

Kuja is more powerful than Beatrix. He is not even human, and it seems that each Summon in FFIX can destroy a city. But Bahamuth hited Kuja with his attack, and nothing happened(with exception of a little blood in Kuja's forehead). Kuja's magic power is greater than Beatrix too.