Reevaluation to Tanks Stances and Related Abilities

[Misha_Tameshigiri]

That's just fiddily math. Defiance increases Maximum HP by 25% and increases Healing Received by 20%. The other stances decrease damage taken by 20%. This is equivalent to increasing both Maximum HP and Healing Received by 25%. Defiance may not decrease the value of the red number, but it is equivalent to taking less damage.

It's not equivalent to taking less damage. It's only equivalent if you are being healed at that exact moment.
Let's look at the numbers.
Tank 1 is a WAR with 120 HP, in their tank stance. They take a hit for 20 damage. They lose 20 hp. The healers are busy DPSing at the time and don't heal the tank. The tank has just lost some DPS for no gain at all.
Tank 2 is a WAR with 100 HP, out of their tank stance. They take a hit for 20 damage. They lose 20 hp. The healers are busy DPSing at the time and don't heal the tank. The tank has gained a slight amount of DPS while not losing out on heals, as there were none.
Tank 3 is a WAR with 120 HP, in their tank stance. They take a hit for 20 damage. They lose 20 hp. The healers are focusing them and they are healed immediately for 20 hp. The tank loses out on DPS, but gains in heals.


In all of these situations, the WAR takes 20 damage.
However, the tank stance is only an advantage in the WAR's case if he is being healed or if attacks are coming in that necessitate a large buffer of HP (read: tank busters).
In the case of PLD or DRK, the tank stance directly reduces all incoming damage, which is functionally equivalent to Tank #3's situation ONLY.