Mercy Stroke pretty useless for WAR?

[BIRDMAN]

If you're thinking of only DPS gains, then stay out of defiance and after every 3 GCD's start up a Storm's Eye Combo. Even if you've spoiled another combo Fracture is the highest potency dealing attack the WAR has (outside of Inner Beast).
If tanking- you can't maintain Storm's Eye at all times. Somewhere in the middle you'll have to Inner Beast, you'll have to begin a Butcher Block Combo, or you'll have to Steel Cyclone. Your priority debuff will be Storm's Path, and even then it allows ample time to Butcher Block Combo (or Storm's Eye), Inner Beast AND apply fracture before having to reapply Storm's Path.

simply put, Fracture (and Inner Beast) compared with all other GCD's possesses the most potency of any WAR skill. As such, it is far from detrimental, especially when tanking. You may aswell tell me what a 10% slash resistance reduction actually amounts to for EVERY skill a warrior has, because I doubt +1GCD and 1ish autoattacks before reapplying SE will amount to more than 300 potency.