I think this is a matter of taste. For example, I went to a huge Karsh retrospective and could not get through it. To me his work was all technique, and just empty. The prints were dramatic, of course. In the next room were maybe a dozen of Avedon's portraits, which also were beautifully printed pieces but in addition had artistic resonance, for me, and conveyed a certain psychological insight. FWIW, I can see others feeling the opposite. It's what you like.
Some of my favorite "portraits" were done by Henri Cartier-Bresson, and with a Leica. They are informal and the opposite of what most people in this thread would consider portraiture, but they teach me something every time I view them.
Did anyone mention Irving Penn? I love his work, and find his corner portraits especially brilliant.