Largely (I think...) agreed.
I think the Tenacity issue is that it does so little defense increase that it's not noticeable. For example, you could fully stack Tenacity, and a single Shellwhetnight of Corundum already increases your defense so much more that you don't even notice the additional Tenacity. They need to make Tenacity allow you to actually skip out on CDs or layer them more thinly, or they need it to do something else. And the only "something else" relevant is healing or damage, and Tanks already do a lot of healing. I think that's why people think it needs to be tied to more damage.
Piety is a weird stat because you either have enough or you have too little, there's not really an in-between. Moreover, some Healer Jobs (particularly AST) don't need it at all given their other MP regen tools. It works best when paired with Spell Speed.
The issue with Spell/Skill Speed is that many Jobs are relying on lining up with their burst combo. For example, GNB's speed can shorten its Double Down...but you're waiting for 1 min anyway before using it, especially in the 2 min burst window. Using it early is generally not an option, or not a good one outside of very niche fight timings. And besides that, you get the PLD/DRK/RDM weirdness (less so RDM, but it's still there) of Skill/Spell Speed not affecting the other of the two.
EDIT:
It also affects SMN's Physic.
Still.
For who knows what reason.
.
In ARR and HW, there could be an argument for it - not a great argument, but AN argument - since Physic and Cure 1 were both cross-class, meaning someone in a non-healer Job could stack Mind to make more powerful heals.
Also, Healer damage spells (Stone, Aero, Ruin, Bio, Miasma) worked off of Int for damage, which is why Cleric Stance swapped Mind and Int stats. I suppose this could also work for ACN/SMN (don't remember if it could pick up Cleric or not...whatever could use CNJ abilities could, so maybe PLD? Though PLD didn't use Int OR Mind...) if they wanted to do some (minor) healing. So those two stats being distinct was relevant at the time.
Now, it's irrelevant since every Job other than SMN with Physic (Everlasting Flight and Rekindle don't use Mind) use the Job's base stat for their potency. While the potency is still less than for a pure Healer since the Healers have the Maim & Mend Traits that increase them further, the potencies on other Jobs scale from their main stat. Like Everlasting Flight scales from Int (SMN's main stat) and Healing Waltz from Dex (DNC's main stat), and so on.
Physic on SMN may be the single spell in the game that doesn't do this. And there's not even a reason for that since it's no longer a shared spell with SCH (SCH only inherits Res from ACN, everything else it has its own version of; you can see this by looking in the Actions & Traits spells and abilities tab, or if you have an old SCH that has the ACN Physic on its bars still, the Physic is grayed out and says affinity for ACN/SMN only). And Vercure on RDM already sales off Int and SMN has Rekindle and Everlasting Flight as it is, not to mention SMN chaincasting Physic would be one of the most ineffective forms of party healing imaginable. So there's legitimately no good reason for this to still be a thing.