Substats are really kind of a nuisance overall.

Crit is the end all, be all of substats and it isn't even close.
SkS and SpS are job specific but because everything is "Unique" it makes using the same gear for each role tricky to pull off effectively; BLM wants a certain level of SpS to comfortably cast their spells but the same isn't true of RDM who benefits very little from the same SpS tier as BLM.
Determination is just kind of a catch-all stat. It isn't terrible, it's just the stat that you accept as better than X alternative (Piety, Tenacity, SkS/SpS).
Direct Hit is almost as polarizing as Crit really, although Crit pulls ahead due to how it scales later on in an expansion and how several jobs/abilities directly benefit from Crit over Direct Hit.
Tenacity, even after some buffs is just worse Determination. Sure, it provides more passive mitigation but the amount of extra mitigation it would need to provide in order for it to be a gain over Determination is so ridiculous that it's practically an impossibility.
Piety is an absolute joke of a substat and is pretty much the perfect example of the Devs neglect in regards to Healers. The change from increasing your Max MP to just increasing the rate you regen MP is a laughable nerf considering that the Regen rate of MP was a % of your Max MP originally so having more MP gave you more Regen naturally and that it allowed for more casting in general; Hell, I remember when BLM's would meld Piety just to get that 1 extra Fire cast into their rotation but ever since it became a Healer exclusive joke stat, it's only use is as an argument to justify whenever a Healer is struggling with MP issues because their toolkit got nerfed in the latest expansion, only for the Devs to buff them later on and make it a moot argument anyways.