The way I found to play a tank is to have only one point in Warfare, one in Polymorth (for the Armour regen) the rest in geomancer for Fortitute.
He had a 1 handed weapon with poison damage (which get heavily increase by geomancy).
So I placed him far up front so the enemy attack him then I bring the rest of the group moves in range.
If the enemy ignore him and try to run to my back line, they wasted a turn so it's good too.
Then for the rest of the combat he helps with knockbacks or destroy armor/magical armour or giving armour to other party members.
But yeah the defensive abilities, I am unsure, however perseverance if you have 20 you regain all your armor after certain CC so, it's a heavy investment but it might be very strong late game.
However I still have to try it but a 2hander with Necromancy as a secondary spec might be a better tank.
You will attract enemy attacks and you can heal yourself with your attacks (works even through decay) and shackle of pain will either stop enemy to attack you or one of them will take damage (and the drain will work for 50%).
