People are too obsessed with being on top of the charts instead of working as a team.
I am a full darkness specced sin. I dont expect to be ontop of the charts, I dont -have- to be ontop of the charts. I do my job.
I use my CC's to interrupt enemies and protect fellow players. I try to be as annoying for my opponent as possible, but I dont delude myself thinking that as a sin my only role is OMGLOLDPS!
My opinion is that sith sins are jacks of all trades.
-Burst DPS (LOLstab!)
-Sustained DPS (LOLdot)
-Tanking (LOLtroll)
They can do all 3 of those, but not as good as classes that are focussed on it.
Sure, I sucked major donkey balls when I first started pvp as a sin. Then I started to L2P.
Read guides, study the skills. Try and find a play style that suits you. Sins are flexible, powerfull and hard to kill. You just need to know what you are doing.
-Sith sin tank