What's wrong with SCH and how I envision a rework

[Ceasaria]

A few mechanicals quirks, or just my 2c.

Summon Seraph has a 120s cooldown, and Angelic Benediction has a 60s cooldown.
Since Angelic Benediction is only useable while Seraph is up, this makes Angelic Benediction's effective cooldown 120s. Unless this is intended to be on cooldown with the 3 other fairy abilities, which either also have long cooldowns (120s) or would require massive gauge (Feo Ul).

- Imagine Angelic Benediction with 120s cooldown. Let's say I use Summon Seraph at 1 min and 3 min in the fight, and Angelic Benediction at 1 min 20. You see I could only use it the next time between 3 min 20 and 3 min 30.
If you delay too much this ability and want to use Summon Seraph as quick as CD is up, you may loose you Angelic Benediction.
Of course what I want is being able to use Angelic Benediction during all the time Seraph is summoned and everytime I call her as soon as she is ready.

Why would you ever want to use Cancel Fey Deployment? As worded, it would put both fairies in play and lock their abilities out, while granting an extra heal on Physick/Science. There doesn't seem to be a reason to cancel it. The current Fey Union locks your fairy in place, locks it on a specific target and has a very short cooldown. It is cancellable because you might need to move it or change target. You do not have this problem with Fey Deployment.

- The fact I want to cancel Fey Deployment is to use principly Summon Seraph, Summon Feo Ul or using a fairy ability now. I don't want to have the restriction to wait for Fey Deployment to end.

Due to the way DoT snapshot in this game, Art of Poison is very poweful. This is because, as worded, the effect will compound:
Cyanide + Arsenic + Miasma II under raid buffs (lets assume a low 10%) = 126 per tick
126 * 1.5 = ~189 per tick (Art of Poison 1)
189 * 1.5 = ~284 per tick (After 2 minutes, Art of Poison 2, keeping DoTs active the whole time)
284 * 1.5 = ~426 per tick (Art of Poison 3)

- Hmmm, not sure if I have understand what you say about Art of Poison, but in no case, it become stronger over the time.
Your current DoT become stronger on the target who you applied Art of Poison. You can see it as a debuff on your target instead of a buff on you. And it works only on the effective DoT. When they end or are refreshed, Art of Poison doesn't work anymore on those DoT until you apply again Art of Poison the next time.

The Science/Steel combo is pretty strange, because it would effectively be another movement tool. 15s duration translates into 3 Sciences and 3 Steels. Using 1 Science and 1 Steel is worse DPS-wise than one Broil III, but better than Miasma II and Ruin II. You wouldn't use it in heal-intensive situations because 'spamming' Adlo (making sure the shield breaks before-reapply) would be more effective, and you still get the same MP efficiency as Physick (1 MP = 1 heal potency).

- Yes for Science/Steel, I have looked at Afflatus from WHM for this. They lose a bit of dps while doing this but they can move and are doing good healing. If you think about efficiency heal/dps, it's worth to use Science/Steel if the fight require some mono healing and moving. It's better than the use of Regen from the co healer plus you aside using Broil III.

As worded, it seems like you will always have enough gauge to use both Seraph and Feo Ul on cooldown. Embrace generate 5 per cast, 20 casts per minute for 100 gauge + 30 from Aetherflow actions gives 130 per minute. Seraph has a 2 minutes cooldown and takes 100 (50 per fairy) for 50 per minute. Feo Ul has a 3 minutes cooldown and takes 160 (80 per fairy) for ~54 per minute. 50 + 54 = 104 < 130.

Sorry if I got any of the math horribly wrong.

- You can remove ~ 6 cast every 2 minutes because of their abilities which will prevent the fairy to cast Embrace.
In the world of dps optimization, you will summon Feo Ul prepull, like maybe 5 sec before the start.
After she disappears, the goal is to have the possibility to summon Seraph around 1 min after.
Then after Seraph disappears, it left 1 min before Feo Ul is up again. You have to use Fey Deployment to increase your gauge gain (if not did before).
During the moment where you Summon Feo Ul around 3 min, you should have 20/20 left if everything is going good.
This 20/20 is here to prevent long cutscene or disadvantageous moments avoiding you to increase you gauge.
PS : I can put my mathematical operations here if you want.

Thanks for your opinion, I hope I have answered some of your concerns. Tell me if you need more explanations ^^