I’m honestly mixed on this mind soothe change.
There’s literally only 10 Holy Priests and 37 Disc Priests over 3200 IO in NA compared to 500+ Shadow Priests over 3200 IO. I regularly get declined on +25s and 26s because people want to stack Shadow Priests + Holy Paladins.
You’re just making already underplayed healers less viable with changes like this. You could give Shadow a nerfed Mass Dispel/Mind Soothe/no double PI and give the full kit to Holy/Disc.