Melding for AST

[Xelanar]

I disagree on DH being 'best', tbh. Unless you are going for really high rankings on a certain website DH is absolutely not needed on Healer and can only offer a gain of about 0,5% over Det.
Especially on Ast you will probably get more out of melding some piety, to make sure you can keep on casting even during MP intense phases.

Oh shoot - I guess I should have elaborated on that more.
Direct Hit does nothing to increase healing. In Stormblood it was fine, seeing how little impact determination had on healing, and how an abundance in Spellspeed would only give me mana issues. If healing strength is an issue in Shadowbringers, determination or spellspeed would be better options I guess. Or piety to increase mana regeneration if lucid dreaming does not provide enough. It all depends on how our new raid content will be balanced in terms of healing output.

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On a more general note: it's hard to give an answer that is true in all cases as it's highly dependend on the type of content, party compositions, how much healing your co-healer can provide ect. ^_^.
A rule of thumb would be using materia to compensate any weaknesses you notice - which can vary from case to case.