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.
Makes a LOT of sense, Matthew. Learning to maintain connection as either nage or uke means having to feel the most subtle changes both in one's own self and in other person.