Just rework the War Record like MOBAs
There's two different categories for damage. "Siege Damage" (Buildings, Guards, Balloons) and "Hero Damage" (Players).
Could do the same for Heals. Then just reward the Top 3 of each category with the best rewards?
Would be 3 of each: Merits, Kills, Player Damage, Siege Damage, Damage Soaked, Healing on Players, Healing on Buildings, Occupations.
Or just screw that and give the whole guild the best rewards... It's a team effort after all. Frontline would be way weaker if the backline didn't do their job properly.