Need help with my Cobra Lash dmg output

Hey guys,
I am following this Cobra Lash build from Esoro: https://www.youtube.com/watch?v=4DyqmI5-RxU

I can confidently clear T12 maps, but when it comes to T15/T16 maps my damage against bosses drops quite hard. In PoB it looks fine tbh, but it just feels way to low in game.

Sure, my int could be higher, but on most of my items I have some T1 or T2 int roll. Is there such a big difference in lvl 19 gems compared to lvl 20 or 21?

I would appreciate if someone could show me some steps to improve this character.

PoB: https://pastebin.com/Yph8S73X