Blackout is for aoe damage and, as someone was saying in another topic, why stay in aoe if you can move out of it? With or without this ability you should not stand in aoe - the reason I didn't even mention it.
While sin has everything you mentioned above most of those are single target. We all know that is rarely the case in a wz. A sin will die 2x faster than a marauder when faced with multiple opponents. I hope you see where I'm coming from.
Le: I got blackout mixed with fade, but the rest stands.
Actually considering you got blackout mixed up for fade means almost none of your argument stands.
The assassin will get burnt down if focused by multiple enemies BUT so will every other class. In fact, the Assassin is one of the best for avoiding that. (Between Shroud and Cloak)