For me, I would suspect that painless techniques don't provide feedback that provides information to the uke about he technique. I am thinking pain is a means of communication. That communication helps in the learning processes where verbal explanations fail. In the learning process of Aikido we often find direct non verbal communication advantageous. Whole concepts and principles are learned almost instantly communicating non verbally. Pain teaches us limits and boundaries. It provides a framework for learning principles and concepts. We can feel what is happening to the body more accurately and more readily, transference of information, than described verbally. Pain can be an instrument that enhances the learning process, it tell us what is happening as a result of a waza is effective, or isn't.
I agree completely about the difference between verbal and non-verbal cues. Physical sensation IN the body is the most direct route. Learning physical behavior is essentially a physical practice. Words can guide but when it comes to manifesting a behavior at will or on demand, it's the awareness of our body which allows for it, and that awareness is not verbal. Words are an abstraction of the thing itself we seek to be aware of...and perhaps that's why so many approaches include some form of the Silent Method.
That said, I disagree with the first sentence I quoted. Painless techniques provide feedback about the technique, it just takes more focus and attention to make sense of it. Pain gives a strong signal, which is fairly clear most of the time. The ideal of long-term serious aikido training, I think
, is to learn how to read "weak" signals clearly.
...If I'm making much sense. I'm a little tired at the moment.