While Christian hasn't been used to his full potential (and to be honest there are dozens of wrestlers who aren't in both WWE & TNA), I think this is more of a transitional phase since his return from TNA. It is similar to when Jeff Hardy returned from TNA, sure he had more of a spotlight put on him when he arrived, but for the first year, year and a half after he returned, he was a mid carder, he feuded over the IC title for most of that time, then being given shots at the World titles yet it was obvious they weren't going to pull the trigger on it at that stage. They built him back up over time & I think they are doing the same with Christian, but only time will tell.
If he goes to Smackdown after ECW disbands he has a shot at making it & a ready made feud set with Edge, if he goes to RAW I see a less bright future for Christian