From my experience as an Astologian, It feels like I am healing way more then every other healer.
I was in Mount Gulg, with a tank that was a bit of a Jerk. He would run in getting giant pulls, I healed him as much as I can, he hadn't died yet, so good so far
But the problem was, I wasn't able to focus on cards, just had to heal him because his health was going down way too fast, so I had to pull all the heals I've had out of my butt.
He continue to do this more and more, until we almost go to the end. He died after pulling the mega load of add ons, mind you I'm spamming heals and shielding him as much as I can,
Lightspeed, horoscope, aoe heal, everything and he died and he says "That was a first." then commence to calling me a bad healer, because he died, got us all killed, from charging in
and pulling giant loads of monsters.
First of all, you should've kept an eye out on your health, I wasn't able to heal as much as I can and I have crit/Det build,
so I'm focusing on healing and healing and healing but his hp was always close to death. That should've told him "healing is not enough atm, need to go lighter."
I explain to him that He's taking all of my attention to even get anywhere but he mocked me.. I only was able to get sets at the bosses.
That's where I could take a break and focus on cards, buffing, aoe buff a lot more, after healing of course.
But imo, healing is not as strong as an AST.

You'll spend more time healing, now, then you will be focusing on anything else and you'll be even more busy then the other two healers.