Just wondering if runeword famine is being overlooked for echo strike build?

All of that added elemental damage seems pretty significant with the way echo strike duplicates it. And your attacks would be extra un resistable; insane physical damage , good magic damage and decent elemental damage of every type?

you're overthinking it
skill is overtuned with enough damage baseline, just add crit and amp demon

This. No need to mess with elemental damage when everything is amped all the time. Even stone skin immunes get mowed down