Oh, that makes sense. You're not talking specifically about countries with federal systems of government, you're talking about countries that have any form of local government in addition to a national government. That's technically not federalism, but I see what you're talking about.
Here's what Wikipedia has to say about this:
In a federation, the division of power between federal and regional governments is usually outlined in the constitution. Almost every country allows some degree of regional self-government, but in federations the right to self-government of the component states is constitutionally entrenched. Component states often also possess their own constitutions which they may amend as they see fit, although in the event of conflict the federal constitution usually takes precedence.
According to the textbook my American Government class uses (We the People, 14th Essentials Edition by Ginsberg, Lowi, Tolbert, and Campbell), less than 15% of the world's countries use federal systems.
No, I don't think that's fair, because 1) I was specifically referring to the relative scarcity of federal governments out of all the governments in the world, and 2) you're moving the goalpost in order to win the argument. You stated:
In reality, your statement was patently incorrect. Federal and unitary governments are not roughly evenly represented across the world's governments. In fact, the percentage of the world's population that resides in a country with a federal system of government is only 38.05%, and that drops to 20.28% if you don't count India, a significant outlier. The total physical area of the world claimed by countries with federal systems is closer to your 50% guess, at 42.53%, but that drops to 29.89% if you don't count the Russian Federation, another significant outlier.
Your claim of roughly even representation between federal and unitary governments isn't accurate by any of the metrics you used: Number of governments, population, and land area. I'm not sure how political/cultural influence can be quantified, but I dispute its relevance.
Sources: I sourced my populations from World Meter, Wikipedia, and Census.gov, and I used Wikipedia as a source for land areas.