I concede to your point, but remonstrate by arguing that <15% of countries by number is not necessarily a useful statistic. I’d argue that the proportion by population, land area and political/cultural influence is a better metric (and I don’t have a source for that but expect by population it’d be closer to 50:50). Fair?

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:

Your wording has a distinct bias of American exceptionalism, since your first sentence is patently incorrect - federal and unitary governments are roughly evenly represented across the world’s 200-odd governments.

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.