I'm doing alot of PvP on my shadow although im not 50 just (41 atm).
I have tried the full tank specc so i know that the dmg output aint the highest. Imo the tank specc feels unsatisfying and dull with the attacks you have to use to make the best dmg you possibly can.
Here's the thing, I'm playing as full infiltration and find it not lacking in survivability but rather balanced and REALLY enjoyable!
Firstly you can pick your fights more or less, which makes for more 1v1's (I love fighting 1v1 ^^ it's thrilling when both players pop cooldowns etc to smash their opponent).
Secondly the burst you can put out is simply insane somtimes, even thought im not 50 yet I've been able to kill a player in merely 5-6 blows when they are at full health.
Lets say the player has 13K which is kinda high when playing vs people under 50.
Firstly you have 2 Clairvoiant strikes = 3k (10k left)
Project = 3k (7k left)
Force breach = 2,5 -2 ES- (5k left)
ST proc, use Shadow strike = 3,5k (1,5k left)
Finish them off with Spinning Strike = 3,5k (DEAD)
Notice that in this fight, all of my abilities did crit. Im just saying it's very possible as a Shadow to smash someone utterly fast. Before you start hating on this example, let me say. When im playing in warzones I know that to get crits through out a fight wont happen. Though i can tell you this, when high on crit chance you will get more crits then you'd imagine considering your crit ratio. (When you are at 50 im sure you are able to have a higher crit ratio then me so you should be closer to nirvana )
So count on 2 abilities criting each fight, hold your breath and hope it will be ST and the finisher. Since that can kill an opponent from 40% if not more.