Overhealing in FFXIV doesn't inherently mean you're playing badly, it usually comes from Medica II which is far more MP/time efficient than any type of heal even if the amount of healing a party needs is barely more than the initial heal. Same with Whispering Dawn. It's only "bad" if you're, say, Cure IIing someone who could have been topped off with a Cure I (and even then that's sometimes just not wasting your Cure II proc!), or if you're wasting heals by throwing heals out on someone who has Regen on and will survive to the next time they get hit by a mechanic.

Try not to look at overheal too much in this game IMO, there are a lot of HoTs and auto-heals that go out. If someone's overhealing in a negative way, you can tell it's in a bad way without looking at overheal %s or anything.