May be I didn't formulated question clear enough - how to deal with the attacks where attacker is committing only real minimum and if attack is not successful disengage immediately? I'd like to discuss very concrete training methods to face such situation.
Teach such attacks in the dojo. Expect students to attack in that way. Welcome and encourage new students with experience in other arts. Never, ever, chastise an uke who succeeds in hitting his partner, even if it was you who got hit.
Really it's that simple, and that difficult.
If someone trains for years and years against ridiculously overcommitted attacks, they will have a lot of trouble handling real attacks. If they see real attacks from day one, they will see such attacks as "normal."
No, of course this doesn't mean that uke should always be trying to take nage's head off. Karateka learn how to attack slowly, but correctly, so why can't we?