For healers I have to say no it's not that useful, it has a long cast time it's more expensive than physick/cure and generally the mitigation is less than you'd get from a cure at 60. I'd say stoneskin is more just there as a pre-buff now before a pull where it's just that extra bit of mitigation and MP regens instantly anyway. Other than that it's purely there as a cross class for PLD where it is actually useful.