
Emphasizing what was said above: Guardian Deity does not equal Personal Belief.
Religion is pretty up in the air in XIV. The Twelve existed. The Twelve might not have existed. They could be actual gods. They could just be myths and legend. They watch over us. They've been dead for years. No one knows. So just because your Ala Mhigan warrior reveres Rhalgr the Destroyer, as would be expected, it's entirely possible that Nymeia the Spinner, if She exists, might favor you because She's got grand designs for your impact on the world regardless of what you happen to believe. Works in mysterious ways, or something.
In short: Don't sweat it, it really exists only for fluff. You get varying +/- 1-3 points in resistances that total in the hundreds meaning they have less-than-margin-of-RNG impact on you.
Religion is pretty up in the air in XIV. The Twelve existed. The Twelve might not have existed. They could be actual gods. They could just be myths and legend. They watch over us. They've been dead for years. No one knows. So just because your Ala Mhigan warrior reveres Rhalgr the Destroyer, as would be expected, it's entirely possible that Nymeia the Spinner, if She exists, might favor you because She's got grand designs for your impact on the world regardless of what you happen to believe. Works in mysterious ways, or something.
In short: Don't sweat it, it really exists only for fluff. You get varying +/- 1-3 points in resistances that total in the hundreds meaning they have less-than-margin-of-RNG impact on you.