Turning off Defiance is something that Xeno does in a VERY situational manner and he even states in that guide that it is extremely difficult to master.

Dropping your tank stance is done for one reason only, to increase your DPS, which as a tank, you should never need to do. If you are looking for ways to boost your DPS as a tank and you are not overgeared for the content and are in progression. You are doing it wrong.