I would say the tensing is extremely exaggerated. I noticed the same group has additional clips on YouTube and was wondering if this was just a training exercise, as Mr. Burke describes below, or a much broader part of their practice. I found a clip where the first attack is with a tanto and a similar practice is done. I think that indicates that the behavior is a disease of their training environment and there likely is no real kuzushi:
Notice that the uke is holding the tanto edge up, and at 5s into the clip raises her body up when nage presses down on her wrist from on top. It is probably not worth giving them too much benefit of the doubt, if that technique is indicative of their practice.
A quote from Dan Harden in 2012 here comes to mind:
Nage doesn't press down on the wrist. That's not where the kuzushii comes from, but it does illustrate the problems in putting clips out. People are always going to judge from their own POV.
Your comments about a "disease" and exaggerated kuzushi indicate that you don't really understand katageiko. This gives a good intro:
But I get that a lot of people find these clips strange.