Tankers always have an unbelievable advantage in PvP: No one cares about them. Since they have so much HP and a huge quantity of P.def, no one actually bothers to first target them since it's quite pointless as long as he's being healed.
Hence, even if Templars deal low damage - which was confirmed already by beta players - no one will try to avoid you since they keep in mind that you are not going to be of any harm. However, you'll be able to freely root and stun people. Stunning a healer for example, is pretty much game over for him.
Also, keep in mind that even if you deal low damage, you'll survive for so long that you might just be able to wipe your opponent.
All this is applied to partyVSparty PvP. 1vs1 should be a different story but... who cares about it when we'll be rolling masses and sieges at the abyss?
