This whole thread is ridiculous. All classes, if they have equivalent gear, are equally viable in PvP. The weakest classes are the full tank classes, but they are already annoyingly hard to kill and are getting some minor buffs. I play a dps sorc as my main, and I usually do pretty well in PvP, but if I get focused (like I should since I am squishy dps) then I die very quickly.
I find that the majority of people who complain about PvP balance have no idea how to play their class. With my character (Varak on Begeren Colony server) I have met both Imperial players and Republic players of all classes and specialties that do well in PvP. I am currently at valor level 53 with a full set of champion gear. Even with cloth armor the highest damage I have ever been hit for was by an Operative for 5600 dmg (I almost pooped myself). People saying that they have been single hit for 8k damage are full of crap.
The key to successful PvP in SWTOR is your DPS focusing damage and keeping people off your healers; I imagine that most of those complaining are level 30s trying to 1 v 1 instead of sticking with the team and focusing on objectives. Healers-if the other team isn't focusing DPS-can easily keep all people within range alive (Eve, I'm looking at you).
How about before complaining you: 1) Learn your class mechanics and skill rotation, 2) Realize that level 50s are about to go into a separate bracket, 3) Use the rock/paper/scissors class mechanics to your advantage.