I don’t think what you are describing existed in default Flight Simulator X. Both Spot and Locked Spot are locked on the aircraft’s heading. The difference between these two options is that Locked Spot removed the momentum when panning the camera, or the gradual transition as it was called in older versions of Flight Simulator.
While it is not something I would personally use, it is obviously important to lots of people so I think it should be implemented. The External camera is severely lacking in customisation compared to the Cockpit or Showcase cameras. I guess a better thread to discuss that would be the following one.