There is no difference in Stoneskin potency anymore between WHM and non-WHMs (the Graniteskin trait was removed and replaced with the barely noticeable "Quick Stoneskin"), so not sure why you brought that up as a point.

It remains what it always was, a pre-fight or between-fight buff for the tank, just like SCH's Adlo (except that Adlo also functions as their "Cure 2")