Although satisfying to launch a special that do lots of damage you’ll need 1-2 healers on any team. Boring? No! Many of your healers will also be amongst your best atackers. Bread and butter of damage is the ones tiles give and many healers have great attack stat and thus tile damage.
Melendor and Sabina are great attackers in that sense. They have the additional benefit of bring dispellers. Boril and Cyprian riposte tanks are no longer scary. Mel and/or Sab remove those nasty effects without taking damage (as Sonya or Caedmon would). Max «Gandalf» and/or Sab asap. Great for Titans, AW, raids and what not.
Another pair of class A 4* healers are Boldtusk and Kiril. They don’t heal as much as Mel/Sab, but they have that in common that they make your team much better. Boldtusk increase attack of all allies for 4 turns by a significant amount. Kiril does the same for 3 turns (slightly less) but also buffs your teams defence. Max both of these guys as soon as you get hold of any of them. They’ll be your buddies «forever» - also after having a bunch of maxed 5* on your team.
Fnal class A 4* healer is Rigard. His cleansing will keep your team alive in raids against nasty DoT heroes like Colen and Kelile. His attack stat is lower than say Sabina’s, so less useful against titans, but a life savior in raids…
Any other 4* healer worth maxing? Nah - Kashhrek can help you maintain a decent number of cups in early game if that’s your cup of tea, but his low attack stat makes him of little use in other parts of the game.
In short, you need a bunch of healers, and you’ll never regret maxing Mel, Sab, BT, Kiril and Rigard