Why my damage is so low?

https://pobb.in/w3MPk9lGgEdD
Why my lightning arrow damage is so low?

same issue. I still don't know the real reason.

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slice master

The PoB numbers are so low because of the settings (its on pinnacle boss and has a long projectile travel distance) but also because the build is missing a lot of vital pieces resulting in an incredibly low accuracy and a bunch of really bad support gems. You do not want to run added x damage gems when you have decent base damage, run stuff like elemental with attacks, elemental pen and so on.