You have a good day too, Gary. I am not sure how you can tell what page I am on. I am training in a different art than is being talked about on this thread. Dan asked how ...so I tried ...but it was not to be so have fun.
I have trained with people that say that Nikkyo couldn't be done on them...what does that prove? Nothing.
I've done Nikkyo on Dan - that is, he allowed me to do Nikkyo on him. There's nothing wrong with that in a guided course of training.
On the other hand, I would think that it would be a no-brainer that being difficult to manipulate would be of value in a martial situation.
Unfortunately, the ukemi model followed in most Aikido dojo doesn't encourage the development of that skill - and it is a skill, that requires conditioning and training.