Unless you specifically need f/2.8 in the 70-200mm range, there's probably not much reason to pick the 70-200/2.8 over the 100-400.
The 100-400 is a ridiculously sharp lens, even wide open, and with the 1.4x TC. The 70-200 just isn't all that sharp wide-open. Possibly not noticeable on a 24MP sensor, but definitely noticeable on a 42MP sensor. Fortunately, for the typical portrait subjects shot wide-open in that focal length range, that may not matter much. But, between 100-200mm, the 100-400 is sharper wide-open than the 70-200/2.8 stopped down to the same aperture.