Tactics change, and so the way battles play out definitely have changed, too.
In an ancient world face-to-face battle, the actual fighting wasn’t that deadly. The phalanx fighting phalanx, or Roman line fighting a barbarian army, was more a matter of attrition in the very front ranks, with men having decent protection from armor and shields, being wounded or killed, giving place to another, or heroically charging into the enemy formation to try to open a breach for their comrades to exploit. Eventually, as the men tired, one side would weaken and give way, the entire battle order would collapse, and as the losers fled, that’s when the killing would really commence, resulting in the lopsided figures we see today, where a few hundred died on one side and 50,000 on the other.
On the other hand, in battles from the civil war to today, most of the casualties are from ranged fire, and so the definite advantage goes to the side with more, longer range, or faster firing weapons.
The tactics of muzzleloaders were geared to the limitations of weaponry. They presupposed a bayonet charge, which in turn presupposed that fire was only really effective at close range.