I think there are some changes that can be done to make the battle actually enjoyable:
1) The AI's battle groups(Infantry, Archer, Cavalry, Horse Archer) are binded with the player's. So if player reassign the battle group of a type of unit, for example the Imperial Recruit, then AI's battle group setting got changed as well. This should be changed in order to make them two isolated system, so that whatever player do, the AI's FG setting stick with the vanilla.
2) In current game you need to press F7 to split a FG which is not very user friendly. I think it would be better to turn the default FG flags(I, II, III...) into a funtion that no longer links to a specific type as Infantry, Ranged, Cavalry... but only links to the hotkey, then add a new tab to the UI right under the vanilla FG flags where you can decide a unit's type(Infantry, Ranged, Cavalry...). By doing this, also make it possible to add more troop types to the game to support more tactic options;
3) I know the devs are going to rework the perk trees of skills, but I have something in mind and would like share it. I think some battle command should not be available by default unless they were unlocked from the Tactic Perk tree. The concept is below:
Shield Wall --> Skirmish --> Skein
Square Circle
As you can see, it let players to choose between Shield Wall/Square and Skein/Circle, and I think it would be nice if let these perks to boost the simulation strength for Infantry as well. Btw, Square and Circle should not automaticly turn itself;
And it adds a Skirmish command for the player to allow the Skirmish performed as if Sergent in Charge but without having them to closing in towards the enemy. The command hotkey for this unlockable perk, can be F4+F2, while making the toggle of Fire At Will to be F4+F1. This perk shall also add simulation strength for Ranged;
4) Add a perk in Tactic perk tree that increase how many FGs a party leader can command, and always force the AI party leader to split as evenly as possible the Infantry, Cavalry and Horse Archers as long as they exceeded a certain amount(if Infantry >=60, split into 3; if Intrantry >=30 & < 60, split into 2; if Cavalry>20, split into 2; Horse Archer do same as the Cavalry).
5) Middle Click the mouse to change the facing direction of the selected battle formation;
6) If ordering troops to form a Circle formation when 2 different FG were selected, put one FG in outter ring and the other in inner ring, issue this command again to switch these 2 FGs' position. A similar logic shall be added for Square and Line Formation as well;
7) When a FG was selected, scoll the middle button to increase or decrease the width of this FG. Same goes when multiple FGs were selected;
8 ) Add a new troop type called Polearm, a footmen formation that AI can have unshielded polearm soldier assigned to. And another new troop type called Shooking Troop, that AI can put greataxe warrior or Falxmen into. This change will allow both AI and Player to make 6) into a good use, providing more protection to these living targets.
9) Add a Shield Up command for FGs that is not in Shield Wall formation. So that units with a shield could better protect themselves even with out forming this formation.
10) Remove some unnessacery command from the game like the "Column".
Edit: These changes will mainly enhance the footmen's performance in the battle, while the cavalry/horse archer in M&B is already better than Total War, so no need to worry about them.