Here's the issue.
Vercure currently 350 potency, every other Vercure if used one after the other is an instant cast.
AST gets Aspected Benefic which is an instant cast 200/150 potency cure. So RDM pretty much gets the strongest instant cast cure in the game currently and honestly, there are easy ways to fix this.
Vercure 350 potency.
DualCast: 150 potency
A simple change like that would limit the overall cure potential of RDM without breaking their ability to keep themselves alive. As for Raise, I'd say double the MP cost if Dualcast is active. So it would be a give an take, use swiftcast rather than dualcast to raise a target but it serves as a way to limit how powerful their support abilities can be compared to other DPS classes.