Interesting find Cloake! (This is Larrdarr btw).
I'm currently in the Madness build myself, I'm optimistic for its longevity, I've done OK in matches thus far, especially if someone gets a heal off on me. Assassin really needs a resistance to stuns, I've found that to be the biggest problem, since Unbreakable will has kind of a long cooldown (jealous the Deception gets the skill to reduce it by 15 seconds).
Currently I've got 4 points in Darkness, 3 in Deception (for the Duplicity skill) and 26 in Madness, and I can manage to stay alive when fighting quest mobs, and I'm finally about to add Talos as a companion, so I'll report back when I hit 50