At every step, we stop ie "not moving at all" - to look at how uke is controlled. If they can escape there is no control and the technique, in our view, is not right.
Hmmm ... maybe we're getting into semantics. I would say that if you pay attention you will notice that although you may have stopped the gross movement, you are still moving and responding to uke. These subtle shifts in your posture are key to making Aikido work, whether you go slow or fast. If you try to really stop moving, you will lose connection to uke and uke will have no difficulty regaining their balance and extricating themselves. Moreover, if you don't learn to notice and work with these subtle movements then you get a situation where it seems to work when you go fast and not when you go slow.
I think that this is what Chuck is talking about when he says, "Tori should be able to change with uke to maintain the control of the sente (initiative)." He's not saying that there is a particular path or stance for doing technique no matter what uke does. He's saying, as I understand it, that it's possible to adjust your technique to stay connected to uke, regardless of speed.
If you are good (or, more specifically, if you are more experienced than uke), you can control the speed of the technique as nage. That is, you can prevent uke from speeding up. On the other hand, if uke wants to speed up and manages to do it, nage had better stay with them or they will lose the technique.