Healing melds..

[Blood-Aki]

You don't need Piety or Acc to be a good healer so there both useless..

I beg to differ about piety, it's no more "useless" then DET or acc on a non sch, keep in mind the more mp you have the more you regen when you use shroud/aether, and the longer you last during intense healing moments, and when you do dps you have mp to spare, it is far from useless. but since you said you never dps that is why you don't run into healing issue, because you are not expending additional MP for DPS, which means even having 12k mp, you likely won't have mp issues.

as for choice there really is no right or wrong answer i tend to like SS the most and then PIE and det as a left over, since my mains are WHM and AST acc is pretty useless to me.