My claim was based on a video demonstration, so it's hardly irrefutable proof, but I did also say that it requires too much force for too little effect to even bother trying. It's not as if it were a claim of superiority.
If this is that one video of the Murrican' lad shoving a katana through a cuirass whilst a longsword fails to do the same, do note that the katana used is a modern one made in America on a weapons show run by Americans for the purpose of promoting American products. It isn't remotely close to being an accurate analogue.
I have no idea if we're thinking of the same one, but I wouldn't be surprised if we were. No brand names were mentioned, but I could easily imagine an add running just before or after the segment.
IMO Knights would win; plate armor > arrows, so long ranged combat would be out of the question and they'd have to close. Upon which point Shield > 2handing a katana (seriously, not having a means to parry or block other than with the blade is a bizarre trait for a warrior and only could have evolved in such an insular culture) followed by pretty much any weapon > lacquer armor.
Lacquer was a treatment for armor, which was usually metal lamellar, or plates. If you think overlapping plates of steel are useless against weapons, then there is no reason for you to think that the knight would have an advantage.
A knight in full plate doesn't usually need to use a shield, and you don't need a shield to deflect an attack, nor do you need to deflect attacks as your sole means of active defense. Both knight and samurai a much more nuanced than a list of armament.
Daily reminder
A sword of any kind is going to be much more durable when it's secured flush against a large dense object, as shown in that image. I've also seen video of a katana cutting bullets in half as they are fired from an M2 machine gun, without any reinforcement, and several of people that in a single draw, cleave though hanging animal carcasses with gross messers. Seriously, if European swords were really as dull as clubs, and Japanese swords brittle as glass, they would have just used and romanticized different weapons.