Obligatory note that this is not how even the most basic healer, the aforementioned Holy Priest, played just 1 expansion ago, wherein even the still-almost-solely-healing-focused meta builds included...And among other non-healing actions that were nonetheless important to your value...
- A (suppressive) nuke attack on a Haste-scaled short CD
- A 1-minute-CD nuke with incap (upgradable to stun)
- A 20s linear AoE CD (fires a skillshot that goes out and then comes back, damaging in both directions - healing and damage)
- Or, 40s radial AoE CD (slowly growing massive explosion - healing and damage)
- Means of generating, through your attacks, additional charges of Holy Fire, which could stack even on the same target
- The ability to cause an enemy's attacks to instead heal their victims up to some (very high) total amount converted
- Or, a super-saiyen mode that allowed you to float around at greatly increased speed, converting your attacks to make them more powerful, instant-cast, and therefore (since they'd normally take up more than a GCD's time) take less uptime each
- Or, another 1-minute-CD AoE 15s-DoT that also caused enemies who attack the victims to be healed
- Or, the ability to distribute three buffs among your allies (MP from attacking, mitigation, and core cooldown recharge rate) per 90s
- Your rushable (each ST heal reduces ST CD's CD; each attack reduces your attack CD's CD) CDs would cause your next heal or attack to deal far greater potency
- An execute skill that can be used earlier at HP cost and on CD
- Buff from damaging enemies in execute range, potentially augmentable for further benefits when killing an enemy with your execute
And that's for your most "vanilla" healer.
- Lifegrip (Rescue)
- Movement buffs (via 3 charges of ground-placed buff-on-pickup or from shielding an ally)
- Purging enemy buffs (spammable ST and AoE on CD)
- Cleansing debuffs on allies (short-CD ST and AoE on CD)
- AoE fear (enhancible, or replacible with an at-range version or a draw-in)
- Incap on undead and demons
- Dominate Mind (controls mob instead of self)
- Soothe Mind (greatly reduces aggro range, allowing party to sneak past)
- Give ally +20% attack speed
- Give ally cooldown reduction on their defensive (think Riddle of Earth, Manaward)
- Give party/raid MP
- Teleporting past enemies in your soulshape (increased movement speed) form would slow them