Question in regards to end game gear (Healers)

[KageTokage]

I don't think any of the healers ever want piety or spell speed if possible; the former because you shouldn't ever run out of MP if you manage your cooldowns and keep deaths to a minimum and the latter because while it increases your healing per second, it doesn't increase your heal efficiency, (Whereas crit/det do both), plus there are only very specific skill speed thresholds that produce a noticeable benefit for all classes in general (Usually by allowing you to fit an extra GCD into a window where a buff/debuff is active).

[Lunali]

while it increases your healing per second, it doesn't increase your heal efficiency, (Whereas crit/det do both)

Technically it does, though not nearly to the same degree. SpS increases the potency of your HoTs.