I actually came to the forums wondering this. I'm new (I played for a very short time a few years ago) with no endgame experience, I can't add much. I can mention the impressions I had going into the game. I gravitated to scholar when I started playing. My impression was that the scholar was a mitigation specialist who, by using shields and the pet, could free up time to DPS a little. A class that required planning to juggle limited charges, a pet and to time shields well. I figured White Mage was the maximum healing option, and Astrologian was able to fill in either role to a lesser extent while making up for the difference with potent buffs. So: proactive vs. retroactive vs. support specializations.

All of the content up to my level has been really trivial to heal, so differences really haven't come out. I wanted to see what was intended for us but it sounds like scholars are having a bit of an existential crisis right now. Honestly, I want to be the proactive mitigation healer going forward, not the pet healer or the versatile healer. I'm sticking with scholar for now, but it's a bit disheartening to hear that a lot of people view the class differently from how I envisioned.