...wrong.
I'm a Guardian Tank spec. I consistently get the highest medals, am the mvp, and generally help rock face. There is no class that, if we're evenly geared, I cannot beat in a 1 on 1. Not that that is what you should be doing anyway.
As a tank in pvp, stop trying to kill people. Just stop. In Huttball, you let someone else get the ball and guard them to the finish line. In Civil War you rush in WITH A GROUP, taunt the whole rest of the group, and then sit on the turret preferably with a guarded healer. Between myself and a good healer, I've held off four sith before just the two of us. On Voidstar, you just stay WITH THE GROUP and taunt as much as you can, guarding anyone that's being heavily attacked.
You can dps pretty will with guardian slash and force sweep. Especially if no-one is paying attention to you. If you can avoid it, though, never attack another tank class, and only attack Sorc/Sages if they're not targeting you. Go for those that are squishy and weak. I generally will attack any mercs I see to stop the tracer missile spam, too. Whatever you're doing though, don't lose sight of your objective just to dps. You're not built for it. You're built to win warzones through supporting roles and mitigating damage for the whole of the team.
And if you're not doing your dailies, do them. Champion gear is on par with fully purple modded out orange gear from dailies. The only difference is the expertise gain. I have a wopping 3 - my shield generator, an implant, and a relic - gears on me that are pvp gear. But I'm fully modded out and have a couple of columi stuff, which is a much bigger gain. Gear makes a huge difference in this game, but especially for Guardians.
All of this is not to say we're fine as we are; we're awful main tanks in pve, only really suited for off tanking. I've done hard modes as the tank reasonably well, but it's much harder then, say, a vanguard. But in pvp? If you play it smart, there's no reason you shouldn't be topping the medal scale - it's actually the easiest class to get medals for - and being a major asset to winning warzones. If you're just looking for a class to kill people, though, you've picked the wrong class, which probably should have been obvious from the start. While it is possible to rock every other class, you have to stun them at every chance, and remember to pop a buff if you need it. All the same, though, the only ones that give me some problems are operatives if they get the jump and assassins if they give the jump. None of the others are too much of a problem.
TL;DR - gave a bunch of advice to learn to play, so freaking read it.