Viper Strike of the Mamba skill sometime hits and sometimes doesnt?

I wanted to play poison for different version of poison. I always people doing insane dps with Mamba skill. On Poe.ninja it says I am doing 2.5m dps, but skill barely does damage? I watched could of youtube vids, most of them are doing well over 10m dps. Can someone who knows about this game, check my build and tell what's wrong with it?

https://poe.ninja/profile/supr34-6405/character/QUEUESTACKERINDC