Please excuse me. I don't want to offend anyone. Really.
I think understanding (or in my eyes misinterpreting) pain as an element of aiki-technique is more something you do on a beginners level then on an advanced level.
This observation may be true, but have you ever asked yourself why? What is The Reason from bio-mechanical point of view?
I believe the best way to discover it by yourself is to go and practice aikido with different styles\federations. Then,suddenly you can discover that the usual way of executing techniques is not good anymore. Your techniques are not working anymore. AND - you can feel a good amount of pain when receiving techniques from advanced students.
My opinion is that more you practice, more perfectly you learn how to anticipate a technique as a Uke to avoid an injury and PAIN. In the other hand Nage is protecting you, and he does it much better when he is advanced student.
So in the end you get an illusion that pain is not needed. It is enough if some advanced
student (6th dan and more) will 'play heavy Uke' - means he will stop to help you. I'm not talking here about resistance or counters - only being neutral. Try it, and you will discover whole new world, new aikido dimension, where all your present convictions about aikido are meaningless.You will have pain to apply technique and he will feel pain from your application.