Ok, I am being a argumentitive.
To use the phrase "when performed properly" IMO states that if you are causing pain you are doing it wrong. I do not think I am doing my techniques improperly because they cause pain. Pain is a part of training IMO. I do not rely on pain as the sole motivation. Taking uke's balance is primary.
People train differently. Styles vary. Content is vastly different sometimes. Even principles, and how they are implemented, can be very different. In the end, I believe that there are many different arts that are called Aikido and can be traced back to Ueshiba - but to me, they are very different arts.
In my art that is called Aikido, pain has absolutely no place, from the start as I said. Personal choice, inclination, and training. Not for everyone. Not right or wrong. But in my dojo, if a technique causes pain, it is being done improperly. In another dojo, that wouldn't be the case - as it might be that there, something that I do might be deemed improper.... etc.