We have gear swaps, why not get the most out of them? If JAs could be enhanced by stats in more than one way, it would create more job versatility that could be changed on the fly unlike merit points. I tried to come up with at least something for every job, even if some would just be flat out rejected.

I would only really expect this to come from +stat and not from character base and to be used in very high amounts of +stat. I would also say that the +stat gear should only need to be on at activation to maintain the effect modifications otherwise this would be pointless. I also think these should only apply to the main job.

WAR - Berserk: STR: increase attack gain, VIT: decrease defense penalty
Defender: VIT: increase defense gain, STR: decrease attack penalty
MNK - Counterstance: DEX: add TP/counter, VIT: decrease defense penalty
(i just took a stab at this one, if DEX is too easy, maybe use MND? like +50MND =1tp/counter or just even a different thing all together)
WHM – Sacrosanctity: VIT: chance of effect lasting two spells (cap it around 50% I guess?), MND: physical defense boost until you take magic damage
BLM - Elemental Seal: INT: increase the radius of AOE spells, MND: increase the max casting range of spells (LOVE ME SOME RESONANCE IN FFXIV)
RDM – Saboteur: INT: enfeeble duration, MND: enfeeble potency
THF – Steal/Despoil: CHR: Increase chance of increasing Treasure Hunter upon failure to steal (up to 100% TH level increase around +75-80CHR, thief can get right around +80CHR in gear) INT: chance of stealing a random stat from the monster(enables despoil’s debuff effect)
PLD – Fealty: CHR: increase the amount of negative status effects that can be resisted (last time I looked, PLD can get somewhere near +110 CHR in gear, so maybe at +100 you can resist death and encumberance, +80 terror, doom and dispel and so on) VIT: Magic damage can recover MP
DRK – Last Resort: Same as Berserk
Nether Void: INT: increase the max stat you can absorb, MND allow absorb- spells to lower the target’s associated stats (ex: absorb-STR can lower a monster’s Attack beyond the STR they lost)
BST – Call Beast: CHR: Transfer number of player job traits to pet, MND: Transfer number of monster job traits to player
BRD – Pianissimo: CHR: increased song duration, MND: increased song potency (maybe Songs+1 at +85 or 90MND and Songs+2 around+115 or 120MND)
RNG – Barrage: DEX: increase the sweet spot range, AGI: increase the sweet spot bonus
SAM – Seigan: VIT: increased counter rate, AGI: increased TP gained when hit
NIN – Issekigan: INT: increased duration, AGI: spell interruption rate down
DRG – Steady Wing: VIT: enhanced stoneskin potency, AGI: adds phalanx to wyvern
SMN – Avatar’s Favor: INT: increased range around pet, MND: increases stats for party members in range (Titan+VIT, Ifrit+STR, etc – Fenrir Max HP, Diabolos Max MP)
BLU – Chain Affinity: INT: increased skillchain damage, MND: spell additional effect accuracy
COR – Triple Shot: DEX: increase critical hit rate and critical hit damage on second/third shot, AGI: Chance to not consume ammo for second/third shot
Phantom Roll/Double-Up: AGI: Increase AOE range, DEX: Decrease AOE range
PUP – Maneuvers: INT: decrease overload chance, MND: increased maneuver duration (+10seconds for every 30MND maybe?) secondly, this puts all that mage gear to work.
DNC – I fear that Tarutaru named Byrth might have a heart attack if I talked about this job. But maybe the max values and decay rates of saber dance and fan dance?
SCH – Modus Veritas: INT: increased effect, MND: increased accuracy
Circle abilities and arcane crest/dragon breaker/etc: CHR: enhances overall effect