Re: Locking/pinning as pain submission...
Wasn't it stated by more than one shihan that O-sensei had a vise-like grip or that his grip was like a vise. And yes he also had the ability to drain your power by being relaxed, but that does not take away the account of the people (Saito, Shioda and Stevens comes to mind) who said that the founder would demonstrate proper grip (vise!!) when he felt the students didn't hold properly.
I think it is safe to say that there are differences in grips and grips. There are also more than one dimension to holding correctly within the framework of attacking within aikido and defending within aikido.
Both (all) aspects needs to be trained separately and disected, but they need to be present at all times.