Re: The point of aikido osae
First off, while uncomfortable I think the aikido osae waza is to establish and exert control over the partner, ceasing the engagement on a point of [obvious] termination. Many of the aikido pins are simply more comfortable versions of Daito Ryu pins, while still maintaining control of your partner. I think many pins are performed from relaxed positions (such as sitting) to maximize a focus on connecting and controlling your partner, not necessary hurting a joint or nerve. Personally, I think osae waza is very difficult in aikido because we need to first understand what can happen to our bodies before we decide to contest our position. I think many aikido people do not understand that martial context.
When I first began escaping aikido pins I felt the pins lacked something. What I found was I lacked the martial education to realize my "escaping" movements actually would have damaged my body if my partner more severely employed the pins. I think the aikido pins allow us to accept the damage nage could cause and understand our role in the exchange, rather than fight a singular movement.
The osae waza is one of the areas I believe O'Sensei (and probably Doshu) softened in the curriculum to make the art safer to practice. I see those DRA guys do pins and I wince right along with uke. But, if you look at the aikido pins, you can see where a few tweaks would put them right back in the "uncomfortable" range. By uncomfortable, I mean screaming and tapping with anything that can contact the ground then quietly weeping when nage releases the pin.
Second, I think there is a big difference between good aikido pins and bad aikido pins. The assumption in our training is that nage can and does demonstrate control in the pin. Every once in a while we need to make sure that assumption is correct. Hence the occasional screaming and sobbing. And yes, good aikido pins can work.