I think the two work together within the world of Final Fantasy XIV because it's not so much a nature healer (Conjurer I think was more nature) but how the elements exist along a spectrum and there being a split divide on the elements between Dark and Light. With White Mage taking the light and Black Mage taking the dark. This is then also carried on into Red Mage who seek to join the two sides of the spectrum together and why much of their mechanics are to two with balancing the dark and light through their respective elements until unleashing light (verholy) or dark magic (verflare). I think to have White Mage move away from that to have much more of a holy focus I think doesn't fit with the theme and feel of a White Mage here. And I miss big rocks, windy spells and the hope they one day bring a proper water-based spell.
I guess also how as a result it doesn't simply feel like it's a holy mage, which we see a lot of out there, it's more about the elements than any kind of divine power and I like that.
Whereas something more purely holy I think works great for Paladin in this game, just like something purely dark would great for Dark Knight.
[Edit]
Actually it might serve me more argument for why they could add Devout as a 4th healer. I suggested the idea of the 4th healer being a good way to move all of the healer design philosophy of 5.0 to a new job so all those who praise this direction have what they want, whilst reverting the existing healers to the design philosophies people already liked who're complaining. I suggest 5.0 WHM's design could be a good basis because it is the best designed of the 3 in ShB, and Devout would fit the position well. Devout would also leave more room for a pure holy class and could relate back more to Krile too. Though some might argue too close to White Mage in someways, but we also got people calling for Geomancer, which is already close to Conjurer and Astrologian and Time Mage, which is also close to Astrologian.