I think the white Esuna indicators are really clear - far more so than most of the game's indicators. If people aren't using the skill then it's most likely because they're used to paying more attention to the ever-increasing number of mechanics on the battlefield itself these days, or because they're conditioned to ignore debuffs after years where they were hardly relevant to anything, or because they have their UI set up to hide too many things in the party list (or some combination of all of these). Some healers probably don't even bother keeping Esuna on their bars. I would personally find it quite annoying if the spell lit up to tell me when to press it because actually paying attention to my party is one of the sole joys left for me in a game where most healing mechanics have been cut to keep things simple; however, if other people are struggling and unaccustomed to looking at the party list properly then it might be better to also use visual indicators on the characters themselves when somebody has a particularly critical debuff. People are well-used to looking out for indicators to run towards/away from party members or other random mechanics at this point, so indicators to clearly announce a cleansable Doom mechanic might help those who struggle with the regular interface. (Just please keep them in the party list too, because targeting allies on controller during mechanics is a nightmare.)

The only time I can recall the indicators not being clear enough for me was in a recent FC run into one of the alliance raids undersized where I was the only healer, because the alliance UI doesn't show debuffs and I had no idea who was afflicted. We managed, but it would have been a lot less stressful if I could actually see what the other alliance members were doing without frantically moving my cursor around. Having the button light up for that wouldn't have helped at all since I still had to figure out who needed the help, but indicators over the heads of those who still needed cleansing would have made my extreme whack-a-mole minigame smoother.

Another issue is that on new content when a DPS has a random debuff applied that can be cleansed, I have no quick way to tell what that debuff does in the heat of battle without a mouse. And the other players themselves rarely check their own debuffs to communicate that to the healer. In some cases it's obvious, where the icon is something that has been used often, but a lot of debuffs use completely unique graphics and I wonder whether they can be designed more clearly sometimes. There are a lot of situations like this where something is only conveyed on-screen (situational pet/mount/gun hotbars/duty commands are the worst) and I have to ask my friends to read the instructions for me. With debuffs I can check them afterwards in the combat log but making the actual icons more explanatory would be a kindness. Even if the descriptions still have extra detail, being able to gauge the severity of a debuff based on its design is helpful - I feel much more competent when I'm cleansing familiar statuses like Paralysis or Doom because I can intelligently prioritize which people need help with that fastest.