I'm certain you don't know what any of those words mean. An arrow is a projectile too, but neither arrow nor a pistol bullet are jack shyt compared to what an intergalactic warrior civilization would be capable of. There's WAY more in common between a bow and a pistol than there is between either one and what the Predator has available. And since when did a 25yo warrior become a "pre-teen"?
Every predator movie is a massive suspense-of-disbelief movie. Every predator movie requires the Predator to nerf himself tremendously for humans to have a fukking chance. It's just the fact that a woman is involved that upsets you.
I remember when The Coli loved this scene:
Going at a Predator with a fukking sword is okay, but using bow and arrows while fighting on your own land that you know is a bridge too far.