Re: Locking/pinning as pain submission...
What are you trying to achieve? To define "good aikido" as "anything that works to dominate the uke" is a bit low level in my opinion. Any time you can get your techniques working effectively without pain, you have just made yourself MUCH more effective against people who are bigger, stronger, and have high pain tolerances. (Which, I guess is what I'm trying to achieve.)
There are some teachers out there that basically figured out how to tear your arms off if you don't comply with them, but this isn't my cup of tea and while I have to respect their ability (or at least the danger they impose) I'm not all that impressed with them.
I find that Gleason sensei is able to throw me effortlessly against my best resistance - especially against the typical wrist turning techniques. When he does, he has a fairly loose grip, there is no pain, and I cannot stop him. To me, anyone who can do that is approaching the ideal and is a lot more inspirational.
Don't get me wrong; there is nothing wrong with knowing how to force a technique, but I personally wouldn't be very interested in a teacher who could not express such power in a soft way - for very long.
As far as pinning goes - I think you should be able to do it without TOO much pain to the uke (which I suppose has a bit to do with their flexibility) - and if you need pain you can generally just apply more pressure against the joint. I guess I'm having trouble imagining when you _need_ to add more pain? Are you trying to torture information out of the uke? It would probably be easier and more effective to tie them up and use hot plyers. But this seems to be going against the "protect my aggressor" theme...