-Along with the low TA generation others have mentioned, I also find the spec seems heavy on the Energy usage. I think reducing the baseline Energy cost of Cull and then re-designing the License to Kill talent to something that would increase TA regeneration would go a long way.
-Some sort of DoT protection would be really, really nice.
-From a pure quality of life perspective, I think Cull is placed too high in the tree. The simple solution is just switching Corrosive Grenade and Cull's positions in the tree, though Corrosive Grenade would make kind of a meh 20-point talent. Kind of a huge step here, but I like the idea of making Corrosive Grenade baseline, moving Cull and Weakening Blast down to 10 and 20 point talents respectively and giving us a new ability at the top of the tree.
-Devouring Microbes is pretty boring and maybe a bit weak for being so high in the tree.