Allow me a moment to gush, but feel free to ignore it.
In Granado Espada, you had the option to run around with any kind of party make-up, and, generally, characters in healing stances were either unarmed or holding a rosario to increase their basic healing potency and defense rating, with no actual means of defending themselves unless they were to arm up (but this would take you out of the healing stances, disabling healing entirely, and was not an option for every character). This meant that other characters would need to protect them and that they couldn't level up on their own, but this was easily circumvented due to the MCC system, which enabled players to make a team of up to 3 characters (which could include a pure healer), and enabled them to create pure healers among other strange character archetypes that most MMOs would stay far away from.
The most "pure healer" of the giant roster of characters was Valeria, who had the most ridiculously potent HP regeneration skills (we're talking, like, 1/3 HP+SP regeneration per second, for 15 seconds, plus 50% magic damage mitigation on a single target, or half that and 30% magic mitigation on up to 5 characters for 30 seconds) and possibly the greatest Revive skill in the game (able to revive up to 12 characters with a single cast, restoring full HP&SP while applying debuff immunity and 10% universal damage reduction for 30 seconds). She was given a single attack skill, but the potency was so weak, and the cooldown was so long, that most players didn't bother leveling it up or using it, even for the possibility of it's stun. Instead, they would keep her busy with healing, cleansing, and buffing.
Of course, Granado Espada is a very different kind of game, but I can't help but always think back to it whenever I find dissatisfaction with a class or character in any (MMORPG) game I've played since. Despite being almost 16 years old, GE continues to be updated, and its roster of characters keeps expanding with new recruitables that offer a unique suite of aesthetics and gameplay while returning to old characters to improve them and keep them relevant..
..Otherwise, yeah, I can't think of anything.