Got a bad link there.
I’m working on a similar-sounding build. Sitting Duck seems to be overpowered a bit right now due to Immobilize reapplying rather than stacking in duration as it should.
I haven’t tried it yet as I’m at work, but just got the idea that the AOE root that Avatar of Melandru (Human Elite) is capable of, might apply LOTS of Vuln in a big area with sitting duck, as Root seems to apply Immobilize repeatedly for a few seconds.