It's good to look at each healer personal Rdps, but it's not the only data that needs to be looked into.
You can always kind of "cheat" the rdps by going with a healer that does all the healing, and the other one all the dps, which is why its always better to take into consideration the "combined healers damage", and with this you can see that the dps depends a lot on the fight and the intensity of the healing.

On E1S, which requires very little healing, the best healing comp is double WHM, whereas on E2s and E3s, the best comp is AST+SCH, and on E4S it is WHM+SCH.

If you take the combined 4 fights, you see that WHM+SCH and AST+SCH does respectively 98.85 score and 98.27 score, which is the closest you can actualy get in term of balance.
What actualy need a good chunck of balance is the Noct AST to be competitive with the SCH, so the combo AST+WHM could finaly get out of the hole its stuck in since forever...