Actually, there is more than mashing B. It took me a few tries to beat it on commando. The trick is the left stick controls.
No matter how fast you are pressing the B button, if you are not holding the left stick in the proper direction, your presses are not damaging the vulture. The final vulture on Commando you have pretty much zero time in order to move the left stick in the proper orientation.
I don't know if the directions are randomized, but play through once and memorize the two directions of the final vulture (mine was up then right). Then before the indicator shows you the direction, go ahead and push the stick and start pressing the button. Once I did that instead of waiting for the indicator, I won my first try.