Black Iris's strength lies in her utility function to trivialise all physical opponents, not her healing strength, which is less than Camilla's healing dps with her maxed out skill if you decide to Skill AW Iris.
Liana can be deployed to instantly heal everyone across the map, and her Skill AW adds regeneration for everyone across the map that isn't affected by any attack debuffs on her, meaning Liana and Gold Angel Eln can heal your party in rare sitautions where an enemy decreases your attack stat until it's complete garbage (Dark Knight Commander's Dark Aura). Liana's utility function is status ailment healing and resistance, which is invaluable against certain opponents like a Vampire Lord (1 hit paralysis) or the self-paralysis of Plat Samurai Momiji and AW Prince's Skill.
Liana's normal function competes with characters like Fedora and Skill AW Ellet, who are kind of better than her when it comes to skill duration or distance for long distance healing.
Healing DPS Ranking (Total HP Until Skill Expires):
Shiho (AW): 566.95 (8920)
Camilla (SAW 3rd): 556.83 (16,742)
Kikyou (SAW): 555.91 (6115)
Saria (AW): 524.29 (13,212)
Eterna (AW): 500.49 (30,096)
Juno (SAW): 493.17 (5392)
Kagura (AW): 488.33 (5860)
Camilla (SAW 2nd): 481.10 (14,465)
Gold Iris (SAW 1st): 462.80 (13,915)
Camilla (AW): 455.49 (16,185)
Paula (SAW): 453.50 (31,856)
..
Black Iris (SAW): 444.97 (35,597)
Comic inspired by the comic, Bleach, where Liana asks Black Iris to guess the range of her skill during Liana's original event:
Swordmasters were introduced after Vampire Lords, but they skipped ahead and did Hermit AW, and are going to do Monkey Sage AW next week. They can skip ahead and do Swordmasters whenever they feel like, so giving you an estimate is a complete and utter guess, especially when they haven't done AW for Chrono Witches, despite them being in this game for almost a year.