I started messing around with my Shadower post-Justice today and I noticed that when I attack monsters/bosses, I get ~18,000 *3 ticks every second from Venom happening to monsters, but their HP bars remain the exact same. I even wait after a while (18k * 3 should be more than enough to deplete any monster's HP by the time it ends... right?) and attack from a prone position and their HP doesn't seem to be affected by Venom at all.
I'm starting to feel like I should reset my SP and ignore that 4th job skill for now and put those points in Dagger Expert instead.