Just to give my opinion in some statements.
Christian was a midcarder at WWE, at TNA he got the gold and the exposure as one of their main guys. I agree he would return at some point to WWE but not right now, he is on his prime at TNA and he has a written contract for 4 or 5 years.
When Christian left WWE didn't lose a great talent. By this I am not saying Cage is not talented, by how could you lose a talent you didn't build properly. He was a midcarder,. He was losing to Orlando Jordan at the time he left WWE.
And Christian was removed of the Main Event scene first of all because as he is now an stablished star, he is being used to push Chris Harris, and because the Main Event will be Samoa Joe and Kurt Angle at least until BFG.