There is the status effect Potency which increases critical hit rate.
There are the Black Mage T1 Merits: Element Potency, which is a +2 MAB bonus.
The Blue Mage T1 Merits: Physical Potency increases the accuracy of physical blue magic by 2 points.
(I think that's what happens.)
in other words, potency means a lot of things in FFXI, and I don't think elemental magic was ever changed to naturally crit, so it seems unlikely that they'd add a spell to be used in strict conjunction w/ M.Crit gear but yknow
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