I know it's a movie and so takes some liberties when balancing art vs science, but the creators of the movie "The King" did some research, read some historical sources, and went to see a few medieval tourneys to get an idea of how to choreograph the action scenes. The way the movie portrays medieval combat is - I think - a good narrative for Bannerlord to follow to get a decent balance between gameplay and realism - in terms of combat, not plate armor.
The movie is focused on King Henry and finished with the Battle of Agincourt. It does a good job with costumes, so you see a mix of plate, mail, and gambeson. Most of Henry's kills are actually with a dagger that he uses to cut and pierce critically exposed areas. Throughout the movie, swords, lances, even maces show that most of the fatalities are a result of exhaustion leading to vulnerability, rather than slicing and dicing through heavily armored foes. There's a scene where a character - Falstaff - in heavy plate armor is trading blows with another, and no one is dying, then a rider comes along and bashes Falstaff in the head with a blunt object, probably a mace. Falstaff removes his helmet and is visibly very shaken, fighting for air after getting the wind knocked out of him. He pulls down the mail from his head and tries to regain his composure. In the scuffle, he has lost his sword. He gets back up and there is no room to move or even turn as both English and French soldiers are pressed against each other. He starts bashing with his arms in frustration as he is helpless in the sea of plate armor.
Then in a following scene, Henry drops his sword and instead goes to his dagger, as the fighting is mostly heavily armored soldiers wrestling with each other. He starts stabbing in the armpits, the neck, anywhere that is exposed. And it takes a while for his opponent to pass out.
There is no sword-swinging bravado save for a few pitched moments. It's a really believable fight. Even the terrain is a factor in the battle. No one is going into a fight gracefully. Even when Henry recovers from the ground after a scuffle, he looks around and freezes up for a moment as he tries to figure out what to do in the mad melee, right before a horse knocks him back down to the ground.
As for plate armor being impenetrable, this is false. Longbows and crossbows were the bane of European nobility, especially crossbows which allowed quickly trained peasants to kill knights. English longbows were famous for nullifying plate armor. Not only do we have videos of this on youtube, but it can be seen in tapestries and historical art of the era.
However, it is not to say plate armor was pointless. Just because two types of weapons can render it obsolete, not only is there a high chance of not being hit, but the chances of the wearer encountering the many other weapon types made plate usable even up until the 20th century. To this day, plates are uses in body armor to high-enough effectiveness that it can make the difference between penetration or not. Nobles and warriors were known to carry their plate armors with them everywhere they went, even if they weren't going to use them most of the time. It was so valuable, that just having it meant you were richer than most. Another good depiction on the big screen of this that comes to mind is the movie "The Mission" where Rodrigo carries his armor with him everywhere, and even while trying not to drown while being carried down a fast-moving river, spends all his energy on trying not to lose his armor because it is his entire estate's worth in the New World.
Anyways, these are all things you just don't get from Bannerlord, currently. The game lacks depth at this moment, and everything is left up to the player's imagination. I hope TaleWorlds picks up the slack in depth, and doesn't just hope modders will save the day. Especially right now, since their patches regularly pull the rug out from under modders and has resulted in many modders abandoning this game until it becomes more stable.