I'm getting the feeling that you're thinking about the Tank's role in PvP wrong. I don't blame you. When I first attempted PvP, I thought my class was useless. PvE aggro mechanics had trained me to think of tanking in one way and one way only, and without an aggro bar I thought that I was suddenly useless except to stun lock players for a measly 4 seconds. You learn to think differently the more you play.
In seize, Tanks basically run interference for the rest of the team. This can be done a number of different ways, but it boils down to one of two. You're either a big distraction, or you're the bait and lure. The bait and lure tactic is by far the most commonly employed (as the distraction method is usually a last ditch effort to save the team by sacrificing yourself. It sucks for you, but it's better to cost the team 5pts than 10+pts). Direct Defense is almost impossible and is wildly impractical in a PvP setting. The only tank even capable of running effective direct defense is a PLD (with Testudo and cover), and even then the defense is limited to a few team mates and only for a short time with a really long cooldown to work with. It's great for those hardcore charges that need some buffing, but otherwise it's not an effective strategy for the vast majority of the match. If you're still trying to run a tank in PvP by doing direct defense than you should consider rethinking your role, and practicing your dip and dives. You will be infinitely more useful to both the Dps and healers.
