Resistance relics are garbage, run a cool down relic. A lot of Zero's survivability comes from enemies not attacking you in deception. If you're struggling with damage, an elemental relic would do you some good. I notice you don't have a rubi, I suggest you go pick one up. Its so easy to go into deception to hold the rubi and chuck grenades at enemies for full heals. Killing blow is better than Iron hand by a Long Shot, but I don't think ya should be in that tree at all at level 43. I go for middle tree, dealt Mark, Blossom, and ambush are all such amazing skills and all fit his playstyle perfectly, depending on the weapon I'm using I skip two fang. Then I go for left tree for killer and headshot mostly. As well as bore of course.