IMO, nage needs to attack the attack and take
uke's center while keeping their own - in essence, they become the attacker and stay that way until they decide to stop the exchange - uke has no say in it while their center is not theirs. Sounds pretty simple and logical - but not all that easy; first, nage needs to learn how to control their own center before they can go off in search of other centers to control - I think someone once said that aiki starts at home, etc
As my former jo sensei once said (after I said, "You make it look so simple!"): "It IS simple. It ISN'T easy."