Not sure if it work, but i think if this job exist, it will be too OP since now every party only need 1 tank in their party rather than 2 thank, to main reason of 2 tanks is for tank swap, so if there is a job that can change other job into tank than why bother with it 2 tank while that job can just changing partner after tank swap

Beside forcing an DPS player play a tank role is kind of annoying, i rather have pro tank for hardcore raid than half-baked tank that try to do as much damage as possible because of their parces