Looking at your Passive tree, Why do you have the extra 15 points in Acolyte? You could take 13 of those points to add "Desolation" and "Contagion Engine". And while "Symbol of Decay" specifies "Shields" I'm not sure if it would work with Catalysts (I'll test it when I get there), but if it does work with Catalysts, you could get +50% Increased DoT from "Symbol of Decay", +100% Increased DoT for 4s after a kill from "Contagion Engine" and an extra +35% DoT from Desolation.
Or are the extra 15 Acolyte points for more survivability?