. Why should nage back up for kata tori? It won't hurt if it lands.
As far as grabs are concerned, I really like the way Kondo Sensei teaches them. They are an attack, because they lead to a throw. So the first time he teaches this in a seminar, he has the uke grab and throw him. He corrects the uke if needed, so that they are doing a proper attack and throw. THEN he goes on to teach the technique, against that attack and throw.
I think aikido often waters down that idea in favor of training "principles" and movement. Sometimes that concerns me, sometimes not.
On balanced attacks:
I've seen way too many people who can strike with bone crushing power and once the lead foot plants, they are balanced. To throw them, you have to adjust your timing, and move as the attack is forming. To call such an attack "uncommitted" is kind of a cop out, in my opinion (no offense). If they can seriously hurt you with it, you'd better learn to deal with it.