Holmgang: Add a huge parry boost (or six second Stoneskin-like effect). If SE reduces the cooldown of Holmgang, adjust the parry boost accordingly. The risk of Holmgang is that if it used as a mitigation move, but cannot avoid an avoidable AoE. This may also build a synergy with a healer who uses Esuna / Leeches to remove the Bind effect.
Fracture: Adjust Warrior trait to have an Evasion Down effect. Less a mitigation move, more a "Warrior = high risk, high reward tank." There are some mitigation risks with a Warrior, but his/her presence may allow for other party members to trade out Accuracy for other stats.
Sometimes I think of the "cyclone" or "storm" as an obstacle to overcome. And in line of that thinking, think Steel Cyclone and Storm's Path.
Steel Cyclone: In addition to its current effect, adds a moderate Parry boost. If you're on top of your health and enmity, you won't need Inner Beast or Unchained, so you perhaps go for the mitigation chance that Steel Cyclone could provide (again, Steel Cyclone independent of the GCD). In AoE situations, this may help survival rate a little since most AoE fests involve melee attacking foes.
Storm's Path: Either adjust the self-healing or replace self-healing for a short duration, lesser "Stoneskin-like" effect. This may be "Absorbs damage equal to 100% potency, duration 15 seconds." If a Warrior is on top of their hate and prioritizes survival, they may be able to make the healer role easier by refreshing Storm Path as a buffer. In conjunction with Berserk, this would improve the absorption effect of the shield, making Berserk a choice between "do damage and gain enmity or self-heal with absorption."