Originally Posted by
Shurrikhan
When the kit is already balanced around having access to a stance-dependent skill (e.g. Inner Beast), that skill is not a bonus of the stance, but merely a weakness of being out of the stance.
Defiance is a gear-scaling stance where the others (Grit and ShO) scale with content, leaving it generally weaker in early prog by comparison.
It does not affect ability-based healing, despite that they are a tremendous portion of total effective healing, especially at critical junctures.
Its 20% increase to HP falls short of the 25% increase to eHP provided by 20% mitigation, and is not immediate where the others are.
Defiance isn't the weakest by any huge amount, but it is indeed the weakest tank stance. That WAR can sacrifice massive potency for a 6-second (let's say, 2.4 GCDs' duration) Rampart just over every 9 GCDs doesn't undo that. Without Equilibrium, it'd scarcely be touched, and even that's available only once per minute. And that, too, is more intuitively gauged as an opportunity cost attached to Equilibrium than an opportunity gained by using Defiance.