I agree that f/22 optimizes the sharpness across the field, but it does so at the cost of absolute sharpness in the center. Check out this mtf graph of a tele-xenar (tessar design) from Schneider:
and look at the last two graphs showing mtf from f/11 and f/22. The f/22 is more uniformly sharp across the field, but absolutely less sharp in the center than at f/11. The difference is so small that it is of no practical consequence, but the fact is that if you want the sharpest possible image in a subject in the middle of your frame, you would be better off shooting at f/11 than at f/22, even with a tessar. But again, in practical terms, it is of no consequence, unless you are shooting with tech pan on your 4x5.