In my opinion, I don't think there really can be a "tank". Your best bet would probably be to look at particular characters, and if you truly want to be able to just absorb damage, stack armor/health/health regen items.
Rook and Oak are probably going to be the two best picks(in my opinion).
I agree that the game appears to be damage based, but I believe that is the purpose of having support characters like Sedna, Queen of Thorns, and the Citadel's Priests.
Moreso, this isn't like one of the MMO's where tanking saves the masses. As far as I'm aware, not a single character offers an ability to take damage for a teammate or something as tankish. Having 4k hit points doesn't necessarily matter when there are three people wailing on your Healer. Your best bet is to have enough damage or control to hold your opponent down or kill them.
My opinion.