Bound Bow is well balanced. You end up having to invest heavily in two differing perk trees to make the best use of it when compared to destruction so on that basis it does more damage and perhaps rightfully so. When compared to a smithing / enchanting bowman, the damage bound bow does is less but they spend more perks to make it happen. Conjuration as a school provides a degree more versitility in that you have access to summons and a perk allowing soul traps without casting so it can be looked at as a cost effective alternative to the crafting / enchanting bowman builds when you really want to tack something else in for your character.

You would also need Illusion in there for silent casting as Bound weapons create noise just like most spells.