The simplest reasoning should be that if tanks get to have a semi-interesting DPS rotation, then healers should as well.

XIV's healers contributing significantly more DPS then in other MMOs is not a good thing when it's mostly indicative of there not being enough to actually heal through. Healers in the average MMO tend to have more offensive buttons, but seldom actually get the breathing room to use them which ends up making their ability to contribute damage much more nuanced and satisfying when it's done properly.