...but Avedon was an exceptionally skilled portraitist. (Never mind the photography part.)
It's [almost] all about YOU, not the camera. Do what you can with what you have. Working on your skills as a portraitist is immeasurably more important than hemming and hawing over what camera is suitable for your work. This means thinking conceptually and visually as one unit, and being able to work with subjects. It is YOU, not the camera.