I came late into this discussion, so I don't pretend to know all what's going on, but I would like to to say something.
I'm a Pure White Mage. Have been since I started this game (and this is my first MMORPG). I can't act like I don't think there's anything missing from the lineup, but at the same time, there hasn't been an RPG where being the healer was ever easy. Healers have the hardest job of them all, precisely because they have to focus on keeping their comrades alive.
The tank might seem like the martyr, but the tank is always given the ability to survive most situations on their own. In a knuckle-down, drag-out confrontation, though, they don't last unless someone's healing them.
The other healing classes, like Astrologer and Scholar, and certain other jobs that also have healing ability, can't focus on team survivability, because that's not their prime role.
The healer, the White Mage, is a pure job, in action as well as name. Survival as a lone White Mage; it's hard. I spent the first chunk of my gameplay on my own, no parties or groups or Free Companies, so I suffered, and died, a lot. A LOT. -.-' And I was told by many I should just cross-job, even a little, just to get the knowledge. But in my eyes, and based on my original intentions for my game career, I only wanted to be the one to patch people up and keep them going, because someone has to. I don't mean to get dramatic about this, like it's real life, but even in video games, the healer is the "bones" of the community (military speak). Without them and their specialization, it's not possible.
I remember seeing someone mention that as long as players make fewer mistakes, other jobs compensate for the lack of a pure healer. That may be true, but there are lots of ways to make mistakes, and lots of scenarios where mistakes get easier to make, even for seasoned players. Which is precisely why I prefer to be Pure White Mage. My job is easy: stand to the side, watch everyone, and keep them green. Put a protective spell and a helpful effect on them now and again, and generally just do everything in my power to make their job a little less stressful. My job is simple and focused. Willpower and wit is often what I've seen get me through my time in the game. Not just this game, but any game with a healing option. (I once played FF 1 with nothing but a team of White Mages; definitely possible). Anything else that helps that (like pumping up my Hand and Field classes to make items/equipment that helps keep players alive) is a plus.
I'm not saying I wouldn't welcome seeing more added to the job to make it more useful, but right now I'm doing fine with it as it is, and we all know how limited it already is.
That being said, my final message to Square Enix: don't take the job for granted. If it wasn't for the local "bones" topping off everyone's HP, player's wouldn't last long enough to enjoy the rest of the game. So if you can, do them a favour and help out the doc.