> You couldn’t just shoot an rpg at all of them

Yes, a single explosive projectile wouldn't be too effective, but consider an RPG round loaded with cluster bombs, shrapnel, or flechettes. Or the good ol' pray-n-spray with small-arms fire. You don't need much kinetic energy to kill a human on a hoverboard (or at least knock him off).

Helicopters put all of your eggs in one basket, but least it's a somewhat armored basket.