Whether you are Diamond, Diamond Plus or Pinnacle on RCI, you automatically receive Elite Status. I am Diamond Plus on RCI but only Elite on X with 58 Captain's Club points. If I want to get to Elite Plus or Zenith on X then I have to earn the required points on X - they are not interchangeable with RCI.
The same is true if you are Elite, Elite+ or Zenith on X, then you only get Diamond status on RCI unless you earn the required points on RCI for Diamond+ or Pinnacle.