From Yoshida himself

[Pinkie_Pie]

Ya'll will get a kick outta this.

https://twitter.com/Larryzaur/status/874820206501167105

[Ametrine]

I think the deal with SB White Mage is the twofold issue of the status that a White Mage in FFXIV needs to be able to function acting solo, while White Mage was always traditionally the squishy heal and buff bot /unless in very particular circumstances,/ such as with zombies. Other times, white magic is supplemented to other character's skills, such as the trend to give summoner characters a list of white magic. White Mages are the OG support job.

So, in an effort to fit that imagery of a powerful, bursty healer, they put all the emphasis on pure heal potential, while dumbing down the DPS.

White Mage in FFXIV is also irreparably affected by 1.0's decision to break the White and Black Mage dynamic and completely forego the elemental wheel, as all White Mage offensive skills (save for Assize) are tied to Conjurer skills.