Luffy as of rn isn't beating BB either, Hancock's done plenty well so far (no mention of Shiryu tho)
Secondly both marines and Kuja pirates were ambushed by blackbeard. So realistically both had to hold off bb pirates.
She turned two commanders into stone which is nice but they are the weaker commanders.
She then had to get saved before getting clapped by bb himself.
The same bb who captured coby was gonna clap boa whom had to be saved yet only coby gets the bad end of the stick