I love the concept of Astrologian and playing it. However, I know already that the job is actually quite weak. Most of the problem comes from just how their numbers are tuned, but there are also conceptual design issues as well.
Astrologian trades off healing power in exchange for buffs, and the buffs just aren't worth it right now. Even Scholar has Selene which provides a consistent 3% haste buff to the entire party that ends up being better than the Astrologian's buffs over the entire fight, even if the Astrologian gets the cards they want.
The haste buff is one of the Astrologian's best cards, and even under optimal conditions (AoE Royal Road ready, Haste card drawn) it's only 5% haste for 15 seconds, compared to Selene's 3% for 30 seconds (far better). You could use Celestial Opposition to boost that to 20 seconds if you have the 2.5 minute cooldown to burn on it. Not only does the AoE Haste card take at least a minute to set up, the duration is lower, and the randomness means it will not happen consistently, unlike Selene. This is all ignoring the fact that both White Mage and Scholar also do more DPS with their spells than Astrologian, providing more damage on that front as well.
Most Astrologians just keep drawing and discarding cards over and over again. That's not a fault of them, but a fault of the job, because they did exactly what the job encourages you to do. Only a few of the cards are consistently worth using, and the rest are extremely situational and/or not even that great when the situation actually calls for them, so you end up just drawing cards over and over again until you get what you want. You could say "just use the cards", but no, that would be bad, because you will waste your Royal Road bonus for when the card you want actually DOES come up. The other cards need to be worth considering, but right now, they're just not in the majority of scenarios, mainly because they can't be better than damage and haste. On top of that, due to many fights in the game requiring periods of burst DPS, it becomes beneficial to just spend the entire fight setting up a damage or haste card in preparation for that moment. In the end, you just draw and discard until you get what you want and hold.
All of this doesn't even mention Nocturnal Sect, which is also in a very poor spot. It's just not worth using over the Diurnal Sect for many different reasons. For example, the Diurnal Sect's attack speed affects a lot more than the heal potency of Nocturnal (for example, Gravity/nukes). The regens of Helios and Benefic stack, and have a much larger total potency than the shields on both spells. Sure, it takes time to apply due to the healing over time nature of it, but the value is there, especially when stacked (it's not necessarily a bad thing that it sustains over time). The shields don't even offer the crit bonus of Scholar's Adloquium and are still weaker. Aspected Benefic is cheaper and instant cast compared to Adloquium, but the action value on it is just terrible, being far weaker than Benefic II and only slightly cheaper. It's in a funky middleground between Benefic and Benefic II, ultimately being worse on MP in exchange for a weak shield, poor value, and instant cast (woopie).
Astrologian could really benefit from changes. If Time Dilation actually affected all the target's buffs (except certain ones like Hallowed Ground), that wouldn't be overpowered and would be much more useful. Collective Unconsciousness needs a buff for Nocturnal Stance, because losing all ability to act in exchange for -10% damage taken on the party is terrible. Lightspeed needs changes because it hurts your spell potencies far too much in exchange for the cast time reduction that it's not even worth using; you just end up crippling yourself.
I know there's a lot of threads on this already, but I really want to hammer the point home, hoping SE takes feedback into consideration. I really like this job, but I also don't want to be second-rate.
Remember, in the end, just because you CAN do some (or all) content on Astrologian, doesn't mean it's in a good spot or balanced. They have to push much harder than other healers right now to accomplish the same thing.
EDIT: An analysis of the card buffs. I know not everyone is not playing AST so they can't get the full understanding, so here's a layout of how it looks right now.
Cards are poor because even at best situations, they're calculated to be a 1-3% increase in party DPS. Remember, that's under good scenarios; you need to be really lucky. Selene provides a consistent 3% haste buff, which ends up being better than the cards can be even under these optimal scenarios. That's not even counting the extra DPS Scholar will bring because they simply do more damage.
-Bole: Too random to rely on to survive fights. Ultimately all you're doing is slightly fixing your healing handicap by making it easier to heal the tank, making your job easier. This defeats the purpose of being Astrologian in the first place, as you're not really buffing people or supporting them, you're just easing the healing potency handicap you have for being an AST slightly. Better to burn it with Royal Road for the best Royal Road bonus to combine with Time Dilation, because you won't want to burn Balance for that bonus. It has potential to increase the time you can spam Gravity/dps on pulls, but not by much.
-Spear: Too gimmicky. There's no guarantee ever that whoever you throw it at will even use abilities, and they shouldn't go out of their way to USE abilities outside of proper timings just because the cooldowns are lower. If someone's ability isn't on cooldown (say, Raging Strikes) it's probably for good reason -- they're probably saving it for a burst moment coming up or to synergize into their rotation. Even if you do actually reduce its cooldown, are they even going to need it to be reduced? Will they actually use it again in that extra little time window that it's now up before it would have been, or hold it for when it makes the most sense in their rotation/the encounter? Ultimately it more than likely won't grant an entire extra use during the fight, so what was the point? Even under optimal scenarios, it remains "meh" at best. Better to burn it for the AoE bonus, as you would never burn an Arrow. Of course, you would only do that in an 8 man party, because it's terrible to use the AoE bonus in a 4 man party. It's just a total decrease in value. In a 4 man party, as long as you're not wasting a Royal Road, just use it; otherwise, throw it away. Some people recommend using it on your Luminiferous Aether, but again, that ability should be kept on cooldown anyways (especially if you have the mana problems that most Astrologians say they have), and the card has to pop up in a situation where it won't waste a Royal Road.
-Spire: In the majority of fights, TP is not a problem; even if it was, they wouldn't be relying on *you* to fix it, due to how random the chance of getting this card is. None of the fights are long enough or taxing enough on people's TP in most scenarios, especially now in the expansion. 99% of the time, even if you used it, it would make absolutely no difference; if they weren't going to run out of TP before you used it, they still won't, so what did you accomplish? It's useful in dungeons for physical DPS who spam AoE, but you have to:
1. Have the card ready BEFORE an AoE pull
2. Have a physical DPS that will actually spam AoEs and could benefit from the TP
3. Have the mobs live long enough for it to matter
4. Have it be a larger DPS bonus for them to use that extra TP over just getting a damage boost from balance/arrow
... and then what, you allowed them to use their weaponskill one more time, maybe two if you're lucky? And then you ended up not burning it for the Royal Road, which is arguably a better use for it on something like haste. This card could be decent, but it would be more usable if it was at least a Regain effect, but in the majority of scenarios and fights in the game, it's just not useful. You'll draw it and draw it and draw it in situations where no one will even benefit from the TP, at all (for example, any dungeon boss).
-Ewer: Same situation as Bole really. All you're doing is slightly mitigating your own class handicap if you use it on yourself and making your job easier, instead of supporting your party. You could be burning this for double duration, or using it on someone like the Summoner or Black Mage provided you don't have a good Royal Road buff already that you'll waste (because it would be better to just use it on Balance or Arrow). This card still does have applications; it's not like the mana is bad. You can always make use of mana somehow, just as long as it doesn't negatively affect your ability to use the better card buffs (spoiler: it probably will).
-Balance & Arrow: Both great. Just keep drawing and hope you get one, then use proper card strategy. Hold it in your spread until you get a good Royal Road, then time it up with Time Dilation and/or Celestial Opposition with other people's self buffs/a moment where you need more DPS. Ultimately, if using other cards means wasting a Royal Road bonus that you could be using on these, then it's not worth using those cards, because they're just not good enough in comparison. These cards are ALWAYS useful, and then present opportunities in fights where burst DPS is required for even more usefulness. The other cards are far too situational, or weak for reasons I already stated. I'm not saying that these cards are super amazing, but they're still the best choices we have. Their potency is still far too low to make a noticeable difference in most cases.
All in all, the more you play Astrologian, and the more access to skills you get, the more you realize how weak the buffs really are. The optimal strategy involves just drawing and throwing away cards the entire fight to set up for a crucial card use, like Balance or Arrow on a burst DPS phase, and then holding them until that moment. Because the cards are so random, you can't guarantee that you will get the card again when you'll need it, and you want to keep it for when you're going to need it. Even then, who is to say it will even make the difference, due to how weak they are? Again, Selene is consistent, reliable, and will ultimately result in more DPS, unless you get REALLY LUCKY on your card draws, and you KNOW you're going to get really lucky on future draws that you're willing to use your Balances and Arrows when they're not crucial (before burst DPS moments) because you know you're going to get another one for those crucial, beneficial moments in fights. This is the best way at the moment to squeeze the little value that exists out of these buffs, especially because it allows you to ensure that you'll be able to use it with Time Dilation and/or Celestial Opposition, and optimize the setup you worked so hard through the RNG to acquire.
And that's why the cards are not good right now. They need changes.