Will it help if Astro have slow Effect add to Gravity?

[Archwizard]

Blind for Art of War?

Potentially! Or whatever other pragmatic tactic is thematic for the job.
Art of War in itself doesn't really have a lot of explanation for what it is or how it works, compared to the rather self-explanatory natures of Holy or Gravity.

However, I've been noting that SCH here seems to take queues from the job's history of being a mild Red Mage, utilizing dark-attribute attacks (Broil/AoW/ED use the same red-black color scheme as DRK or most Voidsent, while Bio takes cues from an Umbral aspected DoT from 1.0) as an offset to light-attribute healing. A Blind wouldn't be too much of a stretch if the game ever goes out of its way to explain such attacks.

And then people will compare the CC Component(s) between the three healers and then the worst one will be deemed as the new trash healer. Literally unplayable.

Not really. The act of adding CC would in itself mostly only affect healers in dungeons since most raid content doesn't have applications for AoE skills, much less CC effects. And over the course of spamming any CC effect enemies would gradually become more and more resistant to it anyway, so you better hope the CC helps a lot or pull is over before then.

Besides, CC effects can be tuned to different durations or potencies, and ideally each differing CC would be better suited towards each job kit's own strengths and weaknesses. As I said, stall tactics like stuns and slows would be more effective for HoT-based healing than shielding. A shield might be better paired with, say, direct mitigation or all-or-nothing types of damage prevention.