George S. Ledyard
I think that this is a fundamental misunderstanding of what you are talking about. Being difficult to move is a byproduct of proper training but it isn't the point of the training. In the martial context stopping a technique simply means that the attacker does something else. It's all about kaeshiwaza when we talk about fighting. And kaeshiwaza requires the same joining, the same use of aiki, that all waza requires. The instant you simply stop a technique you have lost the opportunity of reversing it.
So my friend, in his eagerness to feel strong by stopping my technique had thereby made it impossible to counter it in an effective manner and take my center. He simply stopped my technique. When someone tenses up like that, they are like the board being held by a couple guys for breaking. With that level of tension, the strike I do will only have more effect.
Actually there are a couple of different ways of stopping someone's technique. What you describe is one of them, and the problem is that it is the only one that most people in aikido know about. The typical depth of understanding of the concept of resistance extends only as far two levels: complete non-resistance, where you give away your center and let the nage throw you (typically aikido ukemi) or complete resistance, where you do everything you can to stop the nage from throwing you, paying no attention at all to the openings this creates. These are just two poles on a very complex continuum of resistance, and I think most of the interesting training lies in between them.
It's very possible to stop someone without being open and yet without taking it to the level of full kaeshi-waza. But there is a lot more to being able to do this besides just trying to resist. To be quite honest, I have trained with senior-level people (5- or 6-dan) in a certain well-known major organization who have done the exact same thing you described here, so it would make sense that the lower-level people are copying them and doing the same thing. If your shihan only teach the nage side of the practice, and your senior people don't understand the uke side, then it's unlikely that you are going to have your junior people spontaneously learning these aspects of ukemi.