I think it would more be a numbers retuning thing.
Art does the most damage of all the healer AOEs.
Holy: 150
Art: 180
Gravity: 130
Dyskrasia: 170
...which becomes significant for each added enemy. For example, at 5 enemies, SCH is doing 250 more potency than AST would be (yes yes, Cards; that's part of balance). So if you gave SCH additional damage (DoTs), you'd have to reduce Art's damage or increase the other healer AOE damage options to balance them all out again. As some folks (Ty, for example) often point out here, back in ARR, SCH's damage was heavily DoT focused. How they achieved this was the DoTs had higher (relative) potency and Ruin had (relatively) lower. So let's say (for example) right now you do 1/3rd of your damage from Bio and 2/3rds from Broil. In ARR, it was more like 1/4th from Ruin and 3/4ths from all their DoTs added together.
So it's less the other healers would need more damage AOE options (if we ignore for a moment the people wanting more DPS buttons for all the healer Jobs) and more their abilities OR the other healer abilities would have to be retuned. Right now, the reason WHM's Glare and Dia do so much damage is because they don't have Cards (AST) or Chain (SCH), so the raw damage of their abilities is higher to compensate. Same with SGE.