TL;DR: I don't/won't answer your question but I'll talk a lot anyways.

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I'm just confused where are you getting these numbers from? They seem highly arbitrary (3 continents, 750,000 deaths per continent, etc.)

The reason we call them the First World War and the Second World War is because that's what people at the time called them and it's what they've been called for going on a hundred years now. Obviously they weren't the first war that took place across 2+ continents or to involve two powers on 2+ modern defined continents but that's not the point: That's what people called them, it's what they've been called for decades, that's what they're called -- first by the German Ernst Haeckel in September 1914 and again by Charles à Court Repington in 1920. There is no international organization or cabal of historians 'naming' things -- it's just we call it what people call it and things stick.

Another reason, and perhaps the most common modern justification though, is that those wars were European wars which just extended to their colonies which happened to be overseas. They weren't 'global' conflicts in that respect they were localized conflicts with localized goals which just had extended fighting -- every single war you listed fits that bill. Outside of the Mughal Empire in the 7 Years' War they're all European powers. The First World War was the first truly global war which hit every single continent. Japan and China and East Pacific colonies, India, Australia, South, East, North, and West Africa, Eastern Europe, Western Europe, the North Sea, Brazil, Central America, North America. Every single corner of the Earth, all from independent or quasi-independent dominions (Australia, Canada, South Africa, New Zealand) operated as independent military entities and as independent government actors. That had never been done before, ever.

I just find your question itself pointless; I know that's not exactly fair as this is a place for questions and for people to learn but I think your question itself needs reevaulation. You create arbitrary numbers and restrictions for how you define a 'global conflict' and then declare that a 'true' or 'real' world war. To make a point:

• The Eighty Years' War was a war concerning Dutch independence. Some people jumped in and out and it was involved in for instance the 30 Years' War and some fighting took place outside of the Netherlands but the fact is it was a war between the United Provinces & Friends vs Spain & Friends for Dutch independence. That was the goal. It was a war between England, United Provinces, France, the Holy Roman Empire, and Spain -- that's not a 'world war'.

• Dutch-Portugese war is a better option but while it extends beyond Europe with sovereign nations (two)...it's essentially Dutch Republic vs Portugal.

I'm already getting tired of this though as because the rest of your list follows precisely the same pattern. Nine Years' War was basically a religious war and expansionism from Louis w.r.t. Europe that had some light fighting in North American colonies. Spanish Succession War was literally just fighting over the Spanish crown, and the Austrian succession war similarly. These are European conflicts between European powers for European goals and when they do extend globally in some fashion it's so extremely limited it hardly deserves the denoting of 'world war'.

You wouldn't call the Gulf War a 'world war' even though it was the U.S. & Friends (America & Europe) vs Iraq (Asia), would you? It had global participants, significant casualties, etc. It's the same thing here honestly: None of those wars you linked involved the popular participation of everyone everywhere even though they, at times, involved some powers from not-Europe and fighting in not-Europe. A 'world war' is not just who is fighting but scale. No one was unaffected by WW1 or WW2. Yes it was started in Europe but its participants not only went beyond Europe those directly and largely affected were as well. 1.5 million Indians would volunteer to fight, America drafted nearly 3 million people, 40% of the Australian male population would enlist, fighting would occur off the coast of Brazil and just about all of Central and South America would come on the side of the Allies as independent, sovereign states. China would send tens of thousands of men to contribute to trench building and also providing supplies while Japan seized numerous German colonies in the Pacific in blatant expansionism. Africa was a theater of independent, quasi-independent, and European fighting forces that raged throughout the war.

Numerous, global belligerents had numerous goals (America expanding trade power in the post-war world, basically any laundry list of European reasons, Ottomans pushing into the Caucasus' of Central Asia and firming their grip on Egypt in Africa, Germans expanding colonial gains by creating a continuous German state across about all of South Africa, Japan taking control of European pacific holdings and trying to force China into basically a protectorate, Australia/Canada/New Zealand/South Africa all developing national identities and using the war as justification for true independence, dozens of Middle Eastern tribes tearing the Ottoman Empire apart for independence, Slavs fighting for independence and unification from the Austro-Hungarians and the Russians trying to enforce such, etc.

This type of global participation was unprecedented and you will never find a war like it: Belgium, Romania, the United States, Australia, India, South Africa, the Ottomans, Mideastern Tribes vying for independence, Hejaz, Japan, Cuba, Costa Rico, Siam. 65,000,000 combatants would participate in the war and 37,000,000 people would die. It was not a European war between European powers for European goals it was a global war between global powers for global goals with significant global fighting between non-negligible sovereign global peoples -- the African, Middle Eastern, and Asian theaters alone justify this point imo without even touching America or Europe!

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Where I got all these silly ideas from:

Peter Wilson, The Thirty Years War: Europe's Tragedy

John Lynn, The Wars of Louis XIV, 1667-1714

Christopher Clark, Iron Kingdom: The Rise and Downfall of Prussia, 1600-1947

David Chandler, The Campaigns of Napoleon

Hew Strachan, The First World War: Volume I: To Arms (specifically his chapters about 'the Dark Continent', the African campaigns)