Where is the most room for improvement for my assassin BV charachter?

https://www.pathofexile.com/account/view-profile/mbakker/characters

I've been clearing most content and now that Im almost level 90 and got a lucky corrupt on a map that turned it into a Hydra Lair, I figured I would try to kill (what I thought) was the main point of my build in melting bosses.

Well I got melted. and I think it's mostly because my leech with warlords mark just isn't enough to sustain on high level bosses.

between my gear and the skill tree, what is the most effective ways you can see for making this better? Thanks