Why are we talking about demographics anyway?
the biggest problem with this kind of thinking - Yglesias, not you - is how it divides the world into two monolithic blocs
it ignores that India has been a functional democracy for the better part of a century (currently ruled by a right-wing nationalist party, but you could also say that about parts of the West) which generally doesn't get along with China, the many internal tensions in Islam, etc. it ignores any nuances or internal differences anywhere besides West/not West.
like, where are the democracies of Latin America - yunno that big chunk of the world where the U.S. spent decades suppressing democracy in the name of freedom (and corporate interests) in this picture? one imagines presumed, like all of Africa, to automatically be under pernicious Chinese influence
idk it basically seems like an excuse to reconcile cheerleading continued American hegemony with nominally being liberal
nb the CCP totally sucks, but this way of viewing the world was dumb and inaccurate during the Cold War and it's dumb and inaccurate now