They are not required to dps.
Give it just 1 second to listen to this guy (interviewer).
https://youtu.be/5la_nyC5BO0?t=281
Yoshi P is our boss of the bosses, what do you need more than his words itself?
Its just that and only that, just because NPC deal damage from time to time does not mean the whole game balance is based on it.
Heck our game got even a rebalance patch where healers lost one of their DPS skill, and tanks got squisher to enforce healers to heal more, it clearly moved towards healers to heal more, you could see it clearly in fflogs where SCH and AST are dealing relatively a lot less dps than they used to.
Healers are not required to dps, fin, fim, finito, ende, koniec.