Just a few comments.
This does not follow. Just to clarify on your first point. It is not so much that the “experts” strike unerringly, but that landing a blow accurately against an opponent “waiting for a missed stroke to strike” is. The hand is faster than the eye, hence the slow transformation in western martial arts to lighter weapons and a more linear style of fencing. Body avoidance is slower and more dangerous than actively defending onself with the blade.
This doesn’t really have much to do with infighting. If a fencer really wants to close and grapple or use a dagger, he can seize control of his opponent’s blade with a beat, bind, etc and just step in.
I can’t speak for eastern sword and dagger fighting, but I can speak for western. The dagger in rapier and dagger fencing is mostly not used for infighting. You have two weapons, one is forty inches and very fast, and the other is about twelve inches and fast. It is safer and infinitely preferable to work with the rapier. The dagger is used for defense and to control your opponent’s blade long enough to set up a successful attack with the rapier.
As I understand it, the katana is mainly a cutting weapon, so I can see that perhaps there is some desirability to closing the distance with surprise to prevent one’s opponent from getting a good cut in. I also don’t think it is likely that one can parry a katana with a dagger, especially without a robust knucklegard. But if someone can do it, I’d love to see it.
Right, I agree with some of this. Knights did carry daggers, actually. After fighting with the sword and forcing your opponent to the ground, the dagger was often used to deliver the telling stroke. There are many, many dagger techniques in the Flos Duellatorum of Fiore dei Liberi, as well as unarmed defense against a dagger.
However, I suspect that a problem would arise for a samurai who attempted to infight. There are many good longsword techniques to deal with infighting, many of them geared towards smashing someone’s face who is already wearing armor. Lacking heavy armor and a steel helm opens a fencer up to several dangers. Even a gauntleted punch to the face or collarbone is potentially devastating, not to mention the classical pommel smash.
Also recall that is is substantially easier to use a long thrusting weapon at close distance than it is a long cutting weapon. So even if a katana fighter closes in, a longsword fighter can still likely use his primary weapon against the samurai’s dagger.
Like I said earlier, that’s not really my thing. In armor, you wear gauntlets. And in unarmored longsword fighting, well, I don’t think half-swording is all that common. If you do it correctly and wear heavy gloves, you have a good chance of not losing any fingers.