Maybe it would help if we spent a little time defining what we each mean by "practical experience."
Practical experience can mean a lot of different things in different fields. But since we're talking martial arts rather than plumbing or politics, I'm going to define it as experience actually executing the methods of your martial art (kicks, punches, chokes, throws, stabs, cuts, whatever) against someone who is honestly doing their best to prevent you from succeeding while also doing their best to execute their own techniques against you. If you have a different definition, please offer it, but I think it's a reasonable starting point for discussion. I also think it's at least pretty close to what drop bear is referring to when he uses the term.
I'm going to break it down a little further and talk about practical experience in a specific context vs practical experience in a broader context. Specific skills, tactics, and techniques may or may not be transferrable to different situations.
I'm also going to talk a little bit about individual practical experience vs collective practical experience. If a single person has successfully used their art in 50 fights, it tells us something about that individual and possibly a bit about the quality of their methods. If thousands of people have used that art in hundreds of thousands of fights, it probably tells us something more about the effectiveness of the art as a whole.
So, let's look at some examples...
First, let's consider collegiate wrestling. The primary skills and objectives of the art are to be able to control another person's body, to establish dominant grips, control their posture, take them down, move them into the positions you desire, and pin them, while preventing them from doing the same to you. (All generally within the confines of a particular sporting rule set.)
An experienced college wrestler will have participated in hundreds of tournament matches and thousands of sparring matches with well-trained, highly conditioned opponents who are doing their best to shut down all of his techniques and simultaneously impose their own will. He will have many, many incidents where a specific movement worked or did not work and opportunity to reflect on why that happened and how to improve his success rate. That's one individual. Since collegiate and scholastic wrestling are fairly widespread, there is also a fair amount of collective experience that coaches and athletes can draw upon to evaluate what works under what circumstances - literally hundreds of thousands of matches which can be learned from.
That is, of course, in a specific context - a sport with a certain ruleset. Do we have any experience with how those wrestling skills might generalize to a wider context? What about other grappling sports? What about mixed martial arts? What about street fights? Do these skills carry over at all?
As it turns out, there is a fair amount of evidence that they do. Many collegiate/scholastic wrestlers will cross over and try competing in other grappling sports. Many have made it into MMA. Many have gotten into "real" fights outside of a sporting arena. (You can find plenty of examples on YouTube. I personally remember almost 40 years ago seeing a wrestler and a Kung Fu practitioner of my acquaintance go at it - the results were decidedly one-sided.) The general results seem to be - the wrestlers do pretty well. If they want to compete at the highest level of MMA or different grappling arts then they have to adjust their technique a bit, but the fundamentals carry over quite nicely. (In fact, many of us in BJJ are working to absorb the lessons that said wrestlers have to teach us.)
Now, let's take another example. Let's say HEMA longsword (Meyer, Fiore, whatever school, it doesn't matter). The fundamentals skills and goals of this art are to be able to cut or stab an opponent with a sword, while preventing them from doing the same to you. What practical experience would a high-level practitioner have?
Well, they would probably have a fair amount of sparring with blunted swords both in a club and tournament setting, trying to hit without being hit, while using the techniques laid out in historical manuals, and attempting to judge whether the strikes would have been of sufficient quality (proper edge alignment, sufficient force, etc) to inflict a disabling wound if the swords were sharp. This counts as practical experience in the practice of hitting someone with a weapon while preventing them from hitting you. However it should be noted that the quantity of said experience is significantly less, on average, for HEMA practitioners than for collegiate wrestlers. HEMA is a niche hobby, typically practiced by adults with other demands on their time and there are far fewer tournaments available to compete at. There might be a handful of HEMA practitioners worldwide with as much sparring/competition experience as a typical D1 wrestler. However, the competition talent pool is much shallower, so the level of challenge they will have faced in their experience will be less.
Next comes the question of how well the skills gained might translate from the actual context of practical experience (sparring with blunt swords) to other contexts. In this case, the most relevant context might be the actual historical circumstances that the arts were designed for - dueling or self-defense with actual sharp swords. And the answer? We really don't know. There are a lot of variables in a real sword fight that we don't get to experience in sparring. The fear of actually being killed or maimed. The willingness to actually kill or maim another person. Knowing exactly how much of a wound you might inflict with a particular blow you land. Knowing whether that wound would incapacitate your opponent and if so, how long it would take before they stopped fighting and trying to kill you. Having the internal fortitude to keep fighting when you've been wounded and don't yet know how bad it is. Having the experience of actually wearing a sword on your person as you go through your daily life. Recognizing the situations where you might need to deploy your sword quickly and how to do so most efficiently and knowing when not to deploy it and knowing the legal ramifications of using your sword in a society where such weapons are common. That's a lot of stuff that we don't have a good way to replicate - and frankly most of us wouldn't want to. If I had access to a time travel machine or fantasy portal which could take me to a time or place where I could get truly complete practical experience in sword fighting, I wouldn't even consider it. I'll settle for developing my skill at bonking people with a blunt sword while keeping them from bonking me.
Now when you say "one should have obtained 'practical experience' from their koryu training", exactly how much time are you spending actually executing your techniques against someone who is really trying their best to stop your techniques and defeat you?
There you go. That's a bit of actual real-life practical experience. It's something you can learn from. And I'm sure your training did help you.
Now consider. That's one incident, against an opponent who probably wasn't even trained in his weapon. What percentage of your technical repertoire did you have the opportunity to use and test out? Assuming that whatever you used worked successfully, do you feel that you now have a sample size to judge how often those movements will work under what circumstances? Compare that to the thousands of matches a collegiate wrestler has had - all the successes and failures and opportunities to see what needs improvement.
We seem to be having a failure to communicate here. Drop bear asked for live sparring. You presented videos of two-person kata, which is definitely not the same thing. There can be value to two-person kata, especially when you allow for the possibility of a bit of improvisation or resistance to check the technical correctness of the movements. I sometimes use similar drills, although not formalized and standardized the way they are in koryu arts. But they are not sparring. The Tenjin Shinyo Ryu video was entirely cooperative and scripted. The video with Amdur Ellis showing Araki Ryu had a bit more improvisation and testing of structure (especially the bit with the naginatas in the bind), but they were still not really trying to hit each other.
