IMO the people who say deception is bad are the ones that tried it, died a few too many times and then decided it wasn't good because they didn't take the time to learn it well. I played mainly as deception from 1-50 (yes i tried madness and darkness) and while leveling i rarely finished a WZ outside of the top 3. Now at 50 with mainly centurion gear with a few champ pieces i finish 9/10 WZ's in the top 5. Most of the time if I'm having a bad game, it's usually because the other team frequently focus fire's me the second i come out of stealth, which is annoying at times but it's not a common scenario.
Now here's why. Firstly you have to accept the fact that you're squishy, get used to it. Don't go running into a pack of 4-5 enemies and expect to survive because you just won't. To people that say we have no utility/cc, if 3 interrupts, a 4 second stun, a slow with 100% up time, force speed, force shroud and on top of all that the ability to escape a fight every 1 min and 30 seconds isn't enough tools to keep you're character in control of the fight, then I'm sorry but you're just asking for too much.
Now I'm not saying this as if deception is an easy spec to play (otherwise so many people wouldn't ***** about it). You have to know all you're abilities and the best times to use them. The key to playing well as a deception sin is that IT TAKES TIME TO LEARN. Be patient, and when you die learn from it, don't just rage at your computer and cry that your class is underpowered.
As a last thing to add, people have to stop thinking that being squishy means insta-death. Its not uncommon for me to go through a whole WZ with 0-3 deaths simply because of all the escaping tools a deception sin has.