White Mage PSA on Myth Tomes.

[dragonflyseksparade]

snip

You can't precast to account for RNG ground aoes that you must avoid. You cannot precast to account for multiple crit hits in succession. In these scenarios you will absolutely need to spam heal for several casts to catch up. 95% of the precasts that you describe are for precasting Cure I while the tank is at full health, in which case you cancel the cast if the tank doesn't take a hit before completing the cast. If you are talking about precasting for big hits, you're going to be using CDs or swiftcast stoneskin (which does not benefit from det, but does benefit from ss, btw). With divine seal on only a 1min CD, there's no instance where you would benefit by choosing determination gear over spell speed gear.