I’ve said this before in this thread, but I’ll said it again in case someone (e.g. Invictus) want to find out about this.
1) melee weapon has noticeably higher damage per fatigue cost, noticeably higher damage per ammo (usability of weapon). So melee weapon is meant to be the best way to kill enemy.
2) Regardless how high the melee damage is, it might not able to replace Ranged damage, DUE TO THEIR RANGE DIFFERENCE.
3) Not sure if intentional, there are fragile enemy units with special effects (e.g. Necromancer, Lost Souls, Archers). Ranged weapon is best used against them.
4) Ranged support. Did you encounter situations where a brother failed to end an enemy’s life due to poor luck or miscalculation? Ranged weapon has wider coverage and is handy against fragile or weaken enemies, so it can handle this quite well. Oh skeletons please go to hell.
EDIT
5) Terrain advantage(when God of Terrain favors you). E.g. long cliffs that force enemy to detour while you shower them with arrows. This factor is rather minor and unreliable because you have no control over it. Also useless if enemy has necromancer that forces you to go offensive instead of defensive.
This is well put; I agree with all of it.
