I have to agree with the OP, this QoL change should be given to SCH as well. Since it's only castable outside of battle and the only time a SCH would use it is when there isn't a WHM in the party I don't see how it would hurt anybody. SCH stoneskin is still weaker due to the lack of stoneskin trait so why not improve the quality of their lives to?
Last I checked WHM gets an ability called benediction that's a 100% heal regardless of stats but ok.. To me that means if the person you're healing has more hp then you're healing them for more. Whm also gets regen and an AoE mass heal + regen that stacks with the ST regen. Calling SCH OP in comparison to whm is silly in my opinion, the jobs are very balanced at the moment in my opinion.
This is a QoL change for healers so they don't have to single target Stoneskin everybody in the party, I would agree that SCH shouldn't get it if it were useable in battle but it's not.