Charles:
I agree that correct study of atemi and atemi waza can be a great way to improve tai sabaki, timing, ma ai, kuzushi etc. In fact imo objectively effective atemi should incorporate all of the above.
Your idea on how techniques are performed by utilising Uke's grab is interesting, in that if one chooses to exercise free will, one may not decide to keep his hand in his face to avoid getting hit, one may instead counter your technique before the kuzushi takes effect for example. In this case, you are depending upon Uke's pre-programmed response to get your technique to work - great for kata practice, but not necessarily so in trying to achieve objectively effective technique.
People react differently when using their free will, some may counter, others tense up, others will strike with something else, others will collapse - there are many options. I have seen beginners react to the same technique you mentioned by tensing up and trying to turn out of the technique. Unless one's kuzushi is effective, chances are they may be successful in shutting things down, as they have not learnt to "receive" the technique in a particular way, they are still reacting from basic instinct.
Personally, if one's tsukuri is poor, then no amount of atemi will help. Integration and competence in all aspects of initially engaging the attack/attacker is more important to the success of one's technique -and these things are what makes atemi effective as well.
Just my thoughts.
LC
