Perallel line traces for melee damage system?

Hello, I am making a medieval game where I will have some few hundred characters fighting (I’ll use one material for all the characters and merge skeletal meshes) and focusing on performance I was wondering what would be better for damage system.

1- Collision box around the blade.
2- Parallel line trace (line that goes from the tip of the blade to the bottom and detects collisions along the blade). Problem: How to deal with concave geometry? I guess I could also do it for projectiles.
3- I already have a collision sphere over the weapons to check for overlaps for the pick up mechanism, maybe I could modify it (make it only be on top of the blade) to also act as the damage detector. I’m not sure this would work tho.

Remeber I’ll have many characters rendered so I need the best method perfomance-wise.

Thanks.