They are suppose to bring the highest healing to the game. Astro is suppose to be a middle man between the two and bring mini cooldowns to make up for lack of burst or mitigation abilities of the scholar. It does it well and your average potency at 20% will be around 800 followed up by another 500 potency nocturnal aspect is easily on par with anything lustrate and white mage tetra which is what noc is used for. Strong single target migitation. I will be the first to agree noc aspected helios is so bad two normal helios is better. But your aoe healing is not affected one bit and if you go by hps then aspected ben along with helios aspect ends up being majorly overhealing so pure hps cannot be a contributing factor.
ED gets to 994 potency (400 + (600 * missingHealth%)) if your target has 1% of their max health. It is a nice CD that I cherish but this is literally your only burst heal. As a SCH, I have the potential for three in a time spam of 60s with a 1s CD. WHM has Tetra along with Benediction, the only % based heal in the game right now.
Yes you can use lustrate 3 times in a row which is 600 potency heal but with nocturnal you can spam infinitely instant casts 500 potency heals while not having to give up charges used for other mechanics in the scholar toolkit. Unlike every other astro it seems thats bad mouthing noc over trying to use it in the way it should be (not side by side comparison of the 5k scholar shields) as a mitigation and patch healing stance complimenting the white mage. Yes your regen stacks with white mage but our team uses an astrologian and a white mage/scholar and even though we started raiding just two nights ago we almost have Ravana extreme down.
Two other teams I know on my server are in A2 right now and one uses an Astrologian that USES nocturnal and says it does its job if you do not pretend you are a weaker scholar. I feel that Astrologian dps spells could be cheaper to make up for its mana issues (which it does have) almost requiring the astro to use a card cooldown AND another cooldown just to extend their mana refresh ability.
To say that Astrologian weak compared to white mage and scholar is just mis information spread and some of us do not want to see the Astrologian have potency increases because it doesnt need it. Ive seen astrologians parse very well utilizing noc/lightspeed/ben 2 bring both tank from 20% to full in a few casts with a well timed Synastry. Astrologian's have the tools and what they need is to be allowed to be the go between both playstyle healers and not be locked out once combat begins. Shifting from Noc to Ben would solve all issues minus offensive power with mana.
And Synastry being overhealing is just conjecture. If you throw it out recklessly then yes it can be seen that way. Allow shuffle to not double draw same card, change Collective consciousness to let you stance dance while the buff is on with maybe a 60 second cooldown and fix mana issues with astro and that should fix the issues.