18th century wars were more frequent but can't compare to the casualties seen in Europe during the first 15 years of the 19th century. Even Frederick, with his massed musket fire, couldn't even come close.
Unless I am quite mistaken, the Napoleonic Wars had very few technological advances in weaponry over the American War of Independence or the Seven Years War.
The biggest difference was the French Revolution and its "popularization" of warfare, resulting in much larger armies "living off the land," with the inevitable atrocities against the people living on that land.
If you run numbers, I believe you will find that the Seven Years War had equivalent percentages of deaths in battle among those engaged to the wars of Naponeon.
These numbers didn't rise significantly till the American Civil War and the development of the rifled musket and minie ball. Then casualties as a percentage of troops engaged did shoot up, as generals continued to use tactics developed by Napoleon and Wellington long after they were no longer appropriate.