I think a lot of healers just don't know and don't experiment enough. By that I mean, they try to esuna or leech something and it doesn't work, so they assume that's always the case. If you actually heal a lot and run a lot of different content, and you try to clear debuffs every time, you'll learn which you can get rid of and which ones you can't. When I was farming Garuda ex for the pony, a lot of healers new to the fight didn't know they could dispel windbite until I told them.