Originally Posted by
winsock
The reason Grit and ShO are on the GCD and defiance is off the GCD is because defiance doesn't do anything on activation.
For example, let's say for the sake of easy numbers:
* you have 1 hp w/ 20k max hp
* A healer will heal you for 16k
* A tank busters is will hit you for 20k before tank stance
Grit / ShO:
You activating one of these tank stances will allow you to live, just so long as it happens before the tank busters e.g. you could do it before or after the heal. Your hp will be 16001 after the heal, the buster is reduced to 16k.
Defiance:
It must be activated prior to the heal to get any benefit, but you will die regardless. If you manage to activate prior to the heal, you are healed for 19200. You get hit for 20k and die. The warrior equivalent to surviving is using IB, which means one way or another, the activation of defiance must occur before the activation of ShO/grit. Defiance is off GCD, to facilitate the activation of IB, which is on the global.