They have Hallowed Ground which is the top tier of defensive cooldowns.
Don't keep it for an "oh no bad things are happening" moment, use it as part of your planned cooldown rotations, especially in endgame fights.

So they have 6 total defensive abilities when you count everything including role skills.
Uh, 7 maybe if you count Divine Veil and 8 if you count Passage of Arms, though you cannot move during it.
Not to mention the chance of blocking on everything on top of parry chance like other tanks have.

They are very much otherwise the support tank, with skills the help bolster defense of other tanks. For years it's been regarded as the de facto off tank for the purpose, though fight mechanics these days have tanks swapping so much there really isn't a main or off.