Well, with regards to the whole problem of battle scale, it's one of those classic gaming problems that never really gets solved unless you specifically go out of your way to address it: Never split the party.
Much like how characters in this game would wear their plate mail armor to bed, (if they ever went to bed at all...) there is no in-game reason to split up your warband, and leave most of your marching army in town garrisons or at their day jobs if they are some sort of militia. Sure, there's a speed bonus to a smaller band and a price cut on the upkeep, but the costs of maintaining an army is negligible in this game. (Something Medieval 2: Total War actually did nicely - armies are really expensive to upkeep, so it's cheaper to just start levying troops when you need them, then dismiss them when the need is over.)
The only times you are split from your warband, it's actually rather ham-handed and arbitrary in the other direction. (My character is a mercenary captain/noble/monarch who is constantly beset by brigands and possibly also assassins... why does my character walk through dark alleyways with no bodyguards the instant he/she hits every town or village? What king that knows assassins are out for his head goes ANYWHERE without a bodyguard, much less just strolling through town?)
So then, the problem is that if you have a raid on a village, mountain bandits show up with a warband 60 troops of mixed unit type. If you fight a noble lord's full warband, you fight something between 30 and 120 troops of mixed unit type. Even the full mustered armed forces of an entire kingdom tends to be about the same battle size as a bandit unit trying to raid a village they thought was undefended.
So, yes, the real-life warfare of the Middle Ages was a sliding scale of conflict intensity, but Mount and Blade, as well as Total War, really just focus on their limited preferred scope of conflict scale (although I suppose you could say Mount and Blade has two conflict scales if you count the solo battle types).
As much as you might complain about being able to know everything on the field in Total War, or how units respond immediately to orders (and the game truly would benefit from simply having more independent units and orders that have to be conveyed by runner from your general unit, possibly with some fog of war due to general line-of-sight deal... I get tingles...), this game is no better in that regards, it's just that the game doesn't pause for you, and the mini-map has no terrain features on it, and the interface is not as precise. You can still demand "Cavalry, Hear Me!" and they do, even with a small mountain between you and some of the cavalry, and your mini-map tells you the location of every unit on the field in real time.
This game really and truly would benefit from the ability to issue standing orders, and having nothing more than a pre-set number orders you can give based upon your ability to communicate with your troops (red flag means charge, yellow flag means hold ground, etc...), and having players rely upon some sort of pre-planned battle strategies and tactics that convey the messy fog of war.
As for scale, I honestly think of Dynasty Warriors, whose sole claim to fame (other than making RotTK more popular while positively desecrating any historical accuracy that might have remained) was the ability to manage very large-scale conflicts behind the scenes while the player ran around in the third person. Similarly to Total War, they had a hierarchical unit structure where individual soldiers only became simulated when the player was looking at them, and then faded into just the sergeants and troop numbers from further away, then officer locations and simple mechanics for handling the conflict based upon morale and troop strengths when the player wasn't looking.
Basically, it's possible to work with sliding scales of combat sizes, but you need to work with reasons to make the player actually want to leave his/her army behind. Players without a fief can't even choose to split their party if they wanted to, much less have an incentive to try. Marching an army hardly costs anything, and there is no significant reason not to keep your full-sized army of knights tromping around the whole length and bredth of the land doing trading caravan runs.
All of these things, however, require far more dramatic changes to the way in which the game is handled than merely deciding whether or not making freestanding pavises make sense, however.
When we are talking about marching weight, however, I go back to the fact that these guys are still carrying a pretty large tower shield on their backs, already. The mantlets I look up that involve, essentially, a small wooden wall on wheels, would certainly be too much for anything short of a siege.
Now, I'm not even going to pretend that I can go toe-to-toe in specialized historical knowledge on specific weapons and armor, but I do think you can boil this thing down to something that is at least realistic, if not perfectly historically accurate. (Calradia being ultimately fictional and everything...) The tower shields that they already carry are large enough for protecting at least most of the body while reloading a crossbow, and only really require that spike on a swing arm to have it stand upright on its own.
Even if they had a smaller shield that couldn't provide perfect cover, having any sort of portable cover for fighting in open fields would be the sort of sensible thing those crossbowmen could carry into battle, especially if it was still something they could carry on their arm if they had to get into melee, the way that many of these people posting in the suggestion would like to see.
Having a mechanic where these things are fairly flimsy, and could be easily knocked over, even by enemy missile fire, much less cavalry charge, and would require soldiers set them back up or go without cover could also be included.
It's not perfect historical accuracy, which won't satisfy a decent number of players who really enjoy the simulationist aspects of this game, I know, but it would be at least a decent shot at realism, and the closest thing you can get without having to go the extra mile of mixed-arms units with precise combat routines that would require major reworkings of the game.
Regarding "LEGION", that's actually a game I haven't seen before, and that does sound interesting. I'm actually not much of a fan of RTS, preferring turn-based games, generally, although genre mash-ups do appeal to me. I once played a long time ago a computer game called Legions, which was basically a relatively old style of ancient Greek/Roman/Persian era strategy game played by pushing numbered tokens over hexes, and thought that was what people were referring to when they had said something about a Legion game when I read it earlier.