I'm afraid this amounts to saying something without actually saying anything. This statement is so vague as to be meaningless.
You've only just made a statement here. You haven't offered any rationale for it. Do you have one? Why is it a false assumption that pain equals good control. Please note that I didn't actually say this. I asked why painful nikyo=bad nikyo. I have felt very painful nikyo that was very effective in controlling me and locking me into immobility. Is this bad nikyo? If so, why?
If nikyo is effective with pain why is it bad?
Well, this is one perspective on the issue of pain in training. Do you think everyone should hold your view? If so, why?
I have been totally controlled by my late shihan's nikyo and it was very painful! His nikyo "really worked" and it hurt like heck!
Which is what, exactly?
You haven't yet offered any solid justification for what you're saying. So far, all you've done is make assertions.
Is this the sum total of your reasoning behind saying that a painful nikyo is bad? I hope not. Certainly, if avoiding pain in training is one's goal, then you might be right. But if one is seeking to be martially effective, I don't see that painless necessarily equates to effective.
Wow, a lot of questions. Assertions? Yes. I admit they are my assertions. If you read what I said there is no 'avoidance of pain' included and in fact quite the opposite for I pointed out how it is useful in order to learn how to deal with it.
So lets start with assertions. I assert what I said to be true. So you can take it that I am saying that's the basic view to start from. So if one throws away all other considerations first or at least puts them to the side for a moment we may then be able to proceed to reasoning behind said assertions. We may also see that some reasoning has also already been offered.
You ask why painful nikkyo is bad nikkyo. Well very fundamentally pain is not good. So I ask you to look at pain. What is it?
Generally it is a flag, an indication something is not good. Be it a pain in the belly, head or wherever it is a flag telling you something is wrong, something needs addressing. If you are sawing a piece of wood and feel pain in your finger you stop for it tells you something is amiss. Carry on and you will maybe lose your finger. So there is the first piece of rationale. Pain equals something ain't good.
Now you no doubt have heard the expression no pain no gain which tends to glorify pain. Well rather that just jump to the conclusion that equals pain is good it is best to understand what that type of pain is. In body building or weight training it is muscle fibres being broken. So if you understand that then you can see the mechanism involved in increasing muscle mass 'quickly' and understand whay you will feel it.
Next we come to an even more basic to do with pain albeit venturing into the spiritual to a degree. Pain is resistance. This is also more pertinent to the best understanding of what I said above and also to the art of Aikido itself for those who take it seriously in my opinion.
So non resistance leads to no pain. Therefor it is good for uke to practice, to take the opportunity to practice the art of non resistance when receiving such things as nikkyo and they will find, if taught properly, what I say is true.
So, once discovering how non resistance handles pain one can then see that this strange thing called non resistance should be practiced at both ends ie: by the uke and by the nage. A nikkyo done with non resistance therefor gives no pain.
These are fundamental principles extant in Aikido. One of the 'magics' inherent in the proper training of Aikido. So my rationale says that given non resistance is fundamental to Aikido and it gives no pain then those techniques done which include it are good and those without it are not.
Therefor you can have a painful full blown 'inescapable' nikkyo done to you and believe it's good but I say it cannot be. Effective.... yes, if you don't know how to non resist it.
Many people may have been totally controlled by painful this or that and so are led to believe that is good and indeed ultimate. Far be it from the case my friend.
I have met many whose eyes go wide in disbelief when their 'painful' technique doesn't work. Every time bar none it was due to what they believed regarding what they were doing and every time bar none they did believe that pain had a major part to play in the making of the technique work. Thus for them it was at that time a dangerous belief. A bad one.
So apart from my rationale I offer my personal experience for that is all I can. Non resistance is a hard (soft ha, ha) thing to learn but is very real and part of this fine art. I would say it's good to learn it and bad not to, it's good to practice it and bad not to.
There is nothing more painful than certain pressure points. I have found that applying non resistance to even those works.
So far be it for me to say why said teacher used pain to demonstrate a technique at a particular time with a particular student for there may have been a specific reason. However I have met some who considered it normal and indeed necessary and in more than one case to extreme. Alas.