Power concerns God's capacity to bring about whatever is possible and willed. The fact that alternative possibilities are within power does not by itself make one of them actual.
If two different outcomes are both possible objects of power, the selection of one is a question of specification. Considered merely as capacity regarding both, power does not explain the preference.
Will concerns which possible object of power is determined to exist. Affirming divine power therefore does not make a distinct account of will redundant.