Esuna is a must have. There are a number of places you will need it. The fact some duties doesn't require it or dispellable debuffs are not a big deal, doesn't means the skill is unneeded.
Some encounters have even scripted the healers must use it. See the bomb debuff in labyrinth, or the silence trap in potd, as examples.
Even in Cutter's cry, the worm's debuff if not dispelled is a pain to heal, when you do that duty in your level 38 gear. Feel bad for the sch that goes there at 39 and have his dispel locked because it is a lv 40 skill. Dunno if that was nerfed or we just got overgeard, 'tho. The first times I were there, that thing were eating 20% hp off per tick.