Bannerlord's entire combat system is extremely lacking in the 'duel' department. Which is not an accident, as it is clearly designed and optimized for battlefield & formation combat. It works for army vs army, but feels lacking/shallow/simple in 1v1 duels.
So, to answer your question, slow down lmao. Let them implement a proper fighting system for 1 on 1 duels first (if they even want to do so) before even thinking about, like, different fencing styles and such.
Bannerlord is vaguely based/inspired on a historical period when there wasn't really much "fencing". The video is about a much later period in our history, and isn't really applicable to earlier times. As far as I know, there were no fencing schools back then, the same way you'd see them from 15th century onward.
Also, bannerlord is so stiff in the way melee combat works that it doesn't really allow for much in this regard anyway.
Bannerlord's combat is still leagues better than Kingdom Come which is entirely based off of fencing (and feels it!). Suppose the ideal would have variety between savage barbarian swinging and foppish lords.
I picked this video because it looks a bit like we already fight in Bannerlord. They just need to let our guy move a bit faster from the start with the possibility to lunge forward and backward and sideways.
The A.I. controlled soldiers often do a move, where they have the weapon at ready and then slide forward during the hit covering more ground WITHOUT taking a step and hit the target. Can be confusing to see as his outside of range when he starts the swing but still manages to hit because of the slide, sometimes I think he cheats and slides what would be two steps forward.
Here is another video with one cut called "the eunuch cut"
I think people did fence from time to time, their equipment suggest so, but could possibly quickly forget/lose much of it in times of peace. We have seen this in the last 100+ years, where even lessons from the world wars have been forgotten. And this in a time where everything was usually written down.