you cant really say that a lot of his powers shouldn't count because he used the powers of the invincible. thats like saying sephiroth shouldn't count because hes injected with jenova cells.

i agree that kuja wouldn't be able to destroy gaia though.

in a direct fight beatrix definetly wins, but kuja would never think of getting too close to beatrix and would fly a lot and destroy her with magic. kujas is nowhere near dumb enough to lose.