[Updated 8/22/2017]
First some background: I played AST up to R1 Primal Diamond at the start of S3, and off-and on throughout S3/S4. I have played it in custom matches, and in Unranked - Platinum games on Aether and Primal in pre-season, and up to Platinum so far in S5 on Primal with an 83% win rate. With all that out of the way, on to the feedback.
Astrologian right now is the weakest of the three healers. The last round of buffs helped, but it's still not enough. Their biggest issue is related to having no way to protect themselves like the other healers, and having such low healing throughput / no damage mitigation that they have to spam bene 2 to keep anyone alive. These two combined turn into MP problems, even with the new changes to Draw, which now gives +1k MP. They also suffer from lower survivability than WHM and SCH due to having no self-peel abilities and high susceptibility to silence / kb / pull.
As an AST you are either going to be starving for MP the entire game, or have more than you need depending on literal luck of the draw with Ewer. More often than not you are starving. You are mandated to take Mana Draw, Recast Reduction, and MP regen trait, or else you will not be able to sustain at all in the Feast.
For survival, they have Disable, self procs, and Lightspeed but that is the limit of their CD's. Deorbit is friendly-only, and Synastry does not benefit you when being focused. Even if you do survive, good Astrologian's are punished by the MP issues noted above and you or your team dies due to not as much MP regen as other healers.
Disable: Great, but way too long of a cooldown considering how often you actually need it. Reduce the CD to 25s, then it would be much more reliable, however as it is right now it's too long to be used as Astro's sole defensive ability.
Benefic 1 Instant Proc: While this is very helpful in kiting and survivability, it is extremely unreliable since it does not proc off of itself. For example, if you have the proc, cast Benefic 1 again then you lose the proc and do not regain the instant cast buff. If this didn't happen, and you could gain the proc again, then it would be reliable and help a lot with AST survivability. If you further enhanced the proc to not only make your next heal instant, but also reduce the MP cost by 30%-50% (balance pending) then it would also solve MP issues.
Lightspeed: This is basically required to use on cooldown for the AST to not run out of MP, so it eliminates it as a kiting tool and defensive ability. It is solely used as an MP reduction tool.
Deorbit:
1) It does have its uses once you get used to it, however the cool down is far too long given how minimal the benefit it gives is. Reduce the cool down to 30 seconds.
2) It's another ability that you can use to save your team, but does nothing for you if you are being focused. Make it usable on self, and if used then you jump backwards 15 yalms.
3) Optionally, just remove it and give AST something better. This is the preferred option - perhaps a minor KB and very brief stun.
Synastry: Allow Astro to cast Synastry on self.
Ewer: Remove this as a random draw, or give AST the ability to manually draw it and still trigger the cooldown of Draw. Either that, or the Benefic 1 proc MP reduction noted above.