HELP WITH FB KATABASIS SLAYER

Hello I am quite new to the game and I have been playing ruetoos FB Katabasis Slayer.Is there a way for me to improve my build overall? I always get one shot and feel like my damage is not enough. The build just not feel fun anymore. Would appreciate any help

Here is my POB: https://pobb.in/E0rnIddY4zJJ