TC you're conflating RDM's usefulness in a couple optional areas of the game with their usefulness in the rest of the game.

They're useful in places where you're either soloing or operating in a non-traditional party config where you just may not have a healer (i.e. deep dungeons and eureka).

But in regular duties and raids, where there are always dedicated healers, RDMs are much less sought after. As others have said, they shouldn't be healing/raising in those situations. Yes, if stuff hits the fan and there's an RDM available to heal, great. But again, that comes at the cost of less DPS.

I love RDM, and I definitely use it in Eureka. But I don't really use it in duties.