It did seem to me that they went from the outside in with their locks - wrist, elbow, shoulder - in a chain; it seemed distinct from the concept of going for the whole body, or through the whole body, which is how aiki arts work in my limited experience.
The practitioner I was working with was most likely being nice to me as he let me take the option of going to the mat and tapping before he made it hurt.
There are around 10 waza in Hakkoryu's nidan-ge that present an equivalent to nikkyo. Some are outside in, from outward appearances -- but the waza are designed to move from under and over while in, producing kuzushi before the lock is even set. This is why the pain is / can be a secondary motivator: the joints are locked all the way through the uke's frame, the uke is already off balance, so sayonara.