chaos bases have no good rune choice

poison build. found a passable cultist bow and can't justify upgrading it.
I could give it flat lightning, cold, or fire damage, but that's barely going to make a difference for a poison or phys/chaos build.

I could put a phys dmg rune on it but that again isn't going to make much difference. Most of the weapon's damage is chaos, iron rune is a percentage working out to less than 4 damage because of the 14-20 added phys dmg I rolled.

even leech is based on physical damage only.

No good choice - so this base will always be underpowered unless its damage has been scaled to account for that gap?