For me it's a lack of consistency rather than necessity.
DA:O and DA2 - Mages had access to one basic healing spell (DA2 mages didn't have Regenerate but did have Healing Aura as a Spirit Healer). Spirit Healers had a more powerful suite of spells for group healing, keeping party members from dying or reviving fallen members. Potions were never auto-replenished but could be crafted.
DA:I - Mages seem to have forgotten that they knew how to cast basic Healing magic in previous games and despite the many instances of dialogue mentioning Healing magic it is strangely absent in it's most basic form. We do have Revival and the KE has a super combo of Group Revival, Group Heal and Group Regeneration (a little too strong honestly, group revive at 50% health and stamina/mana would have been fine on it's own).
The absence of Healing magic flies in the face of lore along with current and previous games' dialogue. It's been a part of the Dragon Age series from the beginning, even Guard and Barrier mechanics were there just not as health bars. It just seems wrong to me that it's missing so suddenly.
Edit: Most especially since the other mechanics survived in one form or another and were buffed (free health potion refills, Regeneration potion upgrades to heal the entire party, healing grenades (Kolto Bomb anyone?), Guard generation for all classes with crafting and little to no Barrier downtime with the right passives) to compensate for the lack of Healing spells.