Doing the math, the 7DII puts about twice as many pixels on target per square mm than the 5DIII. 5DIII is 25600 pixels per square mm and the 7DII is about 53300 for the same area. How that translates into reach advantage is more difficult to assess because optically there is no reach advantage. You just have more pixels on the target to play with.
Your logic is right in terms of math, and that is what motivated me to be on this thread. In the past we have seen that enough pixel density on the subject is required, but is not enough by itself. To be able to crop better, we also need picture quality. To me, a closer cropped 5d3 picture looked almost as good as a lesser cropped 7d picture. I have high hopes from the 7d mark 2, but only photographers who have both the bodies can confirm if it adds enough value in terms of reach over the 5d3, to qualify for an investment in an additional camera body just for the reach.