Just some things I wish to address.
The legendary godsword Katana...
Here's how it does against chainmail.
https://www.youtube.com/watch?v=RFu11mSutd0
Also, I want to add that during the time Katanas were used, only the edge was made of quality material, the rest was of poor material.
On the otherhand, the Knights longswords were entirely made of quality material. The Katana would likely break if it were to clash with a longsword.
I believe what MM was referring to was this
https://www.youtube.com/watch?v=EDkoj932YFo
Just read the comments on why the video is dubious.
As for speed...
Not saying anyone thought this but Samurai weren't uber acrobats who could pull off sommersaults mid combat.
Samurai would actually likely be slower than a Knight, at least a crusader knight. Samurai had metal plates under the typical leather/chain.
Also, Knights were trained to grapple and wrestle with people in close quarters combat, whereas Samurai would have been fairly small folk. If it got to hand to hand combat, the knight would win unquestionably imo.
Of course, don't just take my word for it. This is what I've gathered during hours of research. Do ye own research if you wish :>
EDIT: I remember hearing that the full plated armour knights would typically wear only weigh as much as a modern fireman outfit.