Yeah, healing on RDM will always be imbalanced.

Either, it's too weak to really be notable, so you'll still run with 2x Healers which will be able to handle everything the game throws at them (Otherwise content is being balanced around RDM being mandatory) leaving it so that RDM's healing skills are just useless. Just like it currently is.

Or, RDM's healing is so powerful that it becomes possible to replace a Healer with a RDM and thus the meta becomes that as RDM would push out more DPS than a healer even with dropping GCD's on the occasional heal.

As such, if you want to entertain the idea of fulfilling the fantasy of White Magic on RDM, it would need to be in the form of non-healing based utility. That isn't to say they cannot have heal skills, just that the balance around their utility must come from something other than healing. For example, if they had something like a form of Aurorastorm as a CD that provided SkS and a HoT in its area, it would be primarily used for the SkS buff but would also still be a healing skill.