Our school has that many countries represented now (and 6 continents!) This was a huge draw for our family as we were living in a very homogeneous area. (And DS has crashed on friends’ sofas in some far-flung corners of the world since then.)
Selectivity varies by a million things, and country is indeed one. But it’s also gender, how much FA is needed, boarding vs day, etc. It’s one of the reasons that single % admitted can be so misleading. But @skieurope is right (as usual) that a weak candidate doesn’t become string by virtue of coming from an underrepresented country.