Yeah, you can think of the Napoleon Wars as "World War Zero", and Napoleon as the Hitler of his time.
As you can maybe tell, the aspect of modernity where mass wars with millions of dead sweep the world because some dictator wants it, is not my favorite one.
The Seven Years' War (1756--1763) has been described as the first true world war:
It involved all five European great powers of the time--the Kingdoms of Great Britain, Prussia and France, the Habsburg Monarchy of Austria and the Russian Empire--plus many of Europe's middle powers and spanned five continents, affecting Europe, the Americas, West Africa, India, and the Philippines.
It was a global conflict that involved all of Europe's Great Powers, but the 7 Years' War just wasn't exceptionally lethal or even that destructive.
On the other hand, the 30 Years' War was much less global in its geography but absolutely devastated central Europe, and caused at least 8 million deaths, most of them civilian. This makes it 10 times or more deadlier than the 7 Years' War.
The older conflict was also a crucial game changer for world history because it led directly to the Treaty of Westphalia and the entrenchment of the modern, much more formalized nation state.
What I'd noted was that the 7YW has been called the first true world war (to my knowledge in Manfred Weissenbacher, in Sources of Power, (2009) https://www.worldcat.org/title/sources-of-power-how-energy-f...), and represents the first time a single conflict and set of belligerents spanned the globe. The argument isn't based on intensity of conflict or consequent significance but areal scope.
Previously, multi-continent conflicts either represented contiguous spillover of generally localised battles (e.g., a few millennia of scrapes between southern & south-eastern Europe and Asia Minor), or what were largely maritime conflicts more properly considered as focused on a body of water, most often the Mediterranean (literally, the middle of the world), positioned between Europa, Asia, and Africa. Notable during Roman times but extending well before and since.
The 7YW represented the first time global force projection, even if weak by subsequent or current standards, was even possible.
Its role in setting up Britain and the English-speaking world for global dominance may well be greater than you're allowing for as well.
Very well, in terms of literal global spread of conflict, the 7YW was undeniably closer to being "the first true world war" but I argue that this is secondary to impact and destructiveness if we're measuring these pre-World War candidates for World War. If global involvement is a candidate, why not also include the American Revolutionary War. It too involved multiple belligerent states and conflict scattered across most of the globe.
The 30YW was on the other hand both fantastically destructive even by modern standards and of huge impact to the whole world even up to the present day. True, it was by no means a literally global conflict and couldn't be claimed as one, but the political systems that it led to were also a crucial factor in both the 7YW happening, and the rise of French power which partly made the latter global: The 30 Years' War was one of the factors that led to the ascendant France which later partly forced the English-Prussian alliance in the 7YW.
France could have perhaps only with difficulty have become such a global colonial and dominant European power had the earlier conflict not slowed the formation of centralized authority in the German-speaking states for decades.
The ramifications of Westphalia still reverberate today, the ramifications of the 7YW less so.
That's not as much of an improvement as you might think... Caesar was absolutely murderous and no stranger to ordering ethnic genocide either.. During the Gallic Wars, his armies butchered off at least a million and a half people, while enslaving a few hundred thousand others, partly for the crude sake of boosting Caesar's political career and paying off his debts. Paving the way for smoother Roman colonization was another benefit of this genocide. These things should remind you much more of Hitler than they do of Napoleon.
Bear in mind also that this was done without modern weapons and killing techniques. Hardly a humane ruler. That Caesar happened to be much more rational and erudite than the German dictator certainly helped his long-term image, but just because 2000+ years of history and some good political observations for posterity blot out the mass murder of civilians doesn't make it any less grotesque.
As you can maybe tell, the aspect of modernity where mass wars with millions of dead sweep the world because some dictator wants it, is not my favorite one.
Still, you're not wrong!