Blue Mage spells use the same formulas that White Mage spells do, with a bit added on or taken off. Changes to ours would probably changes theirs. Then mob power calculations come in - if mobs can heal more they would be more difficult, and so on. Or at least that's two reasons they might not want to change the formula.
BLU magic cures are identical to WHM cures. SE was incredibly lazy with them.

Magic Fruit is Cure V with -200 cure power
Plenilune Embrace is Cure V with -90 cure power
Wild Carrot is Cure III with a small reduction in cure power, don't know off the top of my head

White Wind is the only one that doesn't use a previous cure formula. It's only effected by your maximum HP
floor(MaxHP/7)*2
So you'd want to cure in full +potency and +HP gear.