yefj, you have basic problem with understanding what common mode feedback does. It has no connection to mismatch of currents, CMFB sets/tunes both currents in a way that the main OPAMP will operate in the normal active region, it sets all transistor pairs of the differential circuit to the same desired operating point. If the currents have mismatch it doesn't matter from common mode feedback standpoint, CMFB doesn't amplify the difference, it compares the averege voltage of differential outputs to the referential voltage via an error amplifier.