I genuinely don't know how line battles work.
In video games, especially in modded mount and blade. What happens is that you either line up guys or put them on a overlapping lines on an incline. The moment you see the enemy army trying to go into formation, you pepper them with everything you've got. It's not like they can hide forever because your artillery will also keep them from turtling and dugging in. So whoever has the best guns and manages to fire first generally wins and the enemy just dies by the hundreds in seconds because nobody has shields or armor and you can't outrun bullets.