Re: Locking/pinning as pain submission...
My instructor was watching a Steven Seagal seminar tape and saw that the first four techniques were from Wally Jay's Small Circle Jujutsu. Like most people, Seagal didn't mention where he learned those techniques from, so almost anyone who didn't know about Wally Jay, could assume those were Aikido techniques. I've been thinking this might be how Jujutsu techniques are picked-up and end up being shown as an Aikido technique.
I've seen locking/pinning techniques that used levers or went against the joint. Even though these techniques were shown in an Aikido dojo, I'm unconvinced they are Aikido in origin. They might be Aiki-jitsu in origin, but probably not Aikido.
To "prove" that Aikido techniques do go against the joint, you would have to document a technique that went against the joint. Ideally the documentation would include Budo or other early works on Aikido. Off hand, I can't think of such a technique.
Like Kisshomaru Ueshiba noted, the real difference is the attitude of the practitioner. However everybody isn't in Aikido for character development. Some people just want to kick ass and take names later. People like that are really bad candidates to spend years pondering over the exact way to lead an uke.
BTW the quote was from a section titled Differences between Jujutsu and Aikido