I think it all comes down to players, just like how many people mentioned.
Healers main job is to heal, but this is final fantasy.. and powerful dps spell like "holy" belongs to white mages. Thus, they are capable of dpsing.
However, people shouldn't push healers to dps and say that "you are bad healer", this is silly. I also believe it's not about healers, but player themselves. So... With all the respect, I found this "to and not to dps" funny. Good players know when to kite, dps and heal. By any means, don't take me wrong tho.. I personally believe if there is a chance people should take it.