You might think that rune is the last metal you would use for an arrow. Rune is a magical metal, and it has diamagnetic properties (meaning that it repels other metals, sometimes with force). You don't want to be aiming at a garou berserker, only to watch the arrow arc away from them.
As Vannaka would say, 'your problem is that you're thinking like an amateur'. Archers don't actually WANT arrows to hit other metals: they want to slip into the gaps between armour, puncturing an armpit or neck. The best archers also love a trick-shot, hitting an opponent through a sea of allies. The trick is to use the diamagnetism to your benefit, and that - again, to quote Vannaka - 'comes from the hardest skill of all. Practice'.