lol, my sword skills are nill so I won't attempt to address that. However, I'm not sure that a strong grip equates to white knuckling either. Maybe we are just 'disagreeing' on what constitutes a strong grip. I do know that in grappling a strong grip can be quite useful.
I would say that this is one of the things that makes grappling, grappling. But even then, the muscles in the hand are so small compared to your other muscle groups that if you put them in competition with one another, the grip always loses.
I am not saying that strength is bad or that one shouldn't do conditioning. I am saying that what most people do in their technique is inefficient. It uses way too much energy for the task at hand, attempts to accomplish things that it shouldn't be attempting, (i.e. trying to keep someone from moving as opposed to keepoing a direct connection to their center) and doesn't work against people who really know how to relax.
Janet's description of sticking so that you can feel the partner's center is a good one. Then you can start to create movement that doesn't require much in the way of physical effort.