turning defiance off isnt simply the solution to all this since you lose 25% of your HP where paladins dont lose anything.. turning on defiance does not heal you for 25% of this HP.. therefore its much riskier swapping tanks with the warrior toggling defiance on and off

also, you lose all your wrath stacks by turning defiance off.. sometimes you need a buffer for aggro (steel cyclone) or buffer for damage (inner beast) when swapping so yea defiance switching isnt always the best answer