Change Undraw to Something Useful - like Swap!

[ItMe]

Use mouseover targeting or cycle targets during the previous action's activation.

That's fine for mouse and keyboard, but the problem persists if you're using a controller.
I actually find healing pretty difficult for this exact reason.

[Rongway]

That's fine for mouse and keyboard, but the problem persists if you're using a controller.
I actually find healing pretty difficult for this exact reason.

Are you taking advantage of the default soft targeting? The tank is slot 2 or 4, so if you need to heal them while hard targeting the boss and spamming Malefic, you just need to press [down][down] (slot2) or [up][up] (slot4) during the 1.5s Malefic cast and you're ready to use an oGCD heal, after which your target automatically snaps back to the boss for uninterrupted attacking. If you need to use more than one action on the tank, [down][down][confirm] to hard target them is still easy to do during the 1.5s cast. In light party, DDs are just [up][up] or [down][down][down], still pressable during the 1.5s cast time so that you can card them as soon as your cast finishes, after which your target automatically snaps back to the boss again. Full party targeting definitely isn't as easy as it could be on controller, but the farthest target is five downs away, which can be done in the cast time still.