Maybe look into different Cleric classes or a Thaum/Chrono build. If you like summons, Necromancer increases Missile damage by a lot.
Corsair can increase Missile damage a bit too and pillage, but they’re questionable. Pelt can group up monsters for your friend’s Retreat Shot. I’m not really sure which is the best.
Thaum can increase both your damage so it could work as a support and damager. You could take the rank 7 or 8 classes to have damage.
Chrono can Haste, Quicken which can increase crit rate, and Pass.
Almost any Cleric build could help since you can heal.
Sorry if this is a little vague, I don’t really know how your play style is and which classes you’d like or dislike.