Yeah they should just turn all Indigo Stars into Essence of Deeps that increases damage by a million percent.

Nearly all of the essences are meant to fill in the gaps between roles to allow different roles to either solo or fill in for the others.
Tanks: More damage or healing
Healers: More defence or damage
DPS: More defence or healing

The reason why DPS only get +20% damage while tanks/healers get +40-70% damage, is because DPS already deal 50% more damage than them.