Personally, I think the assassin has a lot of potential, not because of the shrouds per se, but because of the various ways to add more of them. I mean, do any of these analyses take into account the Hidden Insight trick - sneak in and place four shrouds, invoke them on a surprise attack? That's gotta skew the damage calculations rather more than d8 quarry dice will. And that's prime for combining with things like the Master of Poisons stuff which adds additional damage to your first hit of the combat.
I've got a couple of builds on the drawing board which abuse Versatile Master and Velvet Blade Trick to stack massive shrouds - as many as three a round or more. (You can only use the Assassin's Shroud power once per round... but Velvet Blade Trick simply adds another shroud to your shroud target, and has no such limit.) Other races have similar ways to help out their bonus damage in sizable ways - Grave Dust Assassin, for instance, is pretty fabulous, and so on.
As for using daggers or shortswords versus fullblades, I'm not sure the case is so clear-cut as all that. They don't have a lot of multi-[W] powers, so the difference isn't going to come up as much as it would for a class where that's the root of more of their damage potential. And what with the amount of invisibility and concealment they can get, Nimble Blade is essentially a permanent +1 to hit with light blades; even the difference between a short sword and a fullblade is only ~3 damage per [W], so it doesn't take all that much to-hit bonus to match up to that. (And since the fullblade is superior, the fairer comparison is with the rapier, in which case it's +1 to hit for Nimble Blade vs. +2 to damage and high crit for the fullblade. Not a ridiculous comparison at that point.)