We're very much aware that the gun sway in-game is higher than in "real life". This is due to a mixture of both game mechanics and trying to simulate the nerves and fear of a horrible death the soldiers faced on the field.
The majority of weapons of the Civil War were more accurate than the most used during the napolenoics due to rifling/minie balls used. From a gameplay perspective, lowering the gun sway amount when aiming to a degree (for example like it is in real-life) would result in far less lines being able to form and fight. The only other solution to this than a simulated combat environment aiming solution is to downright make the weapons less accurate (which I imagine would make a lot of people upset also). Besides that, unlike similar games, we have realistic bullet ballistic, which would make the line combat even harder, if there wouldn't be gun sway.