Personally i think a lot of the problems and restrictions the game currently has can be solved by becoming more simple and realistic
--the cavalry charge. currently it's a wad of mess, every rider tries to target somebody in front of them in their path, but most of them ends up running into their allies in the back and nullifying the charge. there's too much ai work. they keep fighting after you give the command stringing in from the flanks. it's inefficient, gets your troops killed, messy, and not realistic.
what it should be is charging in a block formation in a straight line at an even pace, only attacking the person directly in front of them not closest to them. and charge through as much as possible then disengage off to the flank. you can give them repeated charge commands and they'll repeat the charge from their current direction. this should be easier to implement than the current system, since the units are already in formation and their collisions are easier to manage if staying in formation
--i'm using a mod that increases battle size upto 2000 and i noticed at a certain point it crashes my game, it's not based on the number of units present, but based on the attack calculations, the ragdoll physics, the fast paced buggy twitches and most importantly, the stupid instant pop up respawn reinforcement system. I even have corpses set on showing all. if i limit the battle size, no matter how many units eventually loads in and ends up dead on the ground, the game doesn't crash.
now obviously, tactics and game play would become more "realistic" if units didn't just run in and kill everything/ die within 30 seconds in a frenzy of blows but everything happened in a more calculated manner and paced out more. this could reduce the number of actions the game processes per minute and reduce lag/crash. ultimately allowing more troops on the battlefield offering a more grand experience. in turn becomes more realistic allowing more employment of tactics in combat.
having larger battle maps, dynamic reinforcement locations (maybe you can sent engineer to build it), and bigger battle size would make the field battles infinitely more enjoyable.