Really surprised nobody has commented on this.
You're absolutely right that Dark Surgeon needs major buffs. After playing all kinds of variations, it's not competitive with other healing builds.
To make it competitive with other builds in raids, there needs to be an enchant that increases or uncaps the number of targets that Circle of Healing can heal.
Also, Dark Surgeon needs Renew support to really compete. Currently, healing with Holy Nova feels underwhelming outside of using it to help AoE large pulls so maybe make Holy Nova apply Renew to allies that it hits. And while you're at it, make renew tickrate scale with energy regen increases so stuff like Vitality is buffing it as well as making Adrenaline Rush an awesome healing cooldown for the build.