Cureskin isn't the only thing White Mage has going for it, but it is pretty darn enormous. It's more or less an extra +25% cure potency above the cap and is exceptionally useful in all situations. It's not even the only thing White Mage brings to the table, which puts White Mage that much further ahead of everyone else.

Seriously, White Mage is so far ahead of the game here that no one else is even a speck on the horizon when it comes to filling the role of healer.