I did some more research and it looks like a large share of the US index funds explicitly exclude foreign-headquartered (other than tax-haven) companies, even if they trade actual share on US markets.
So my premise above was kinda wrong. US markets are still capturing globalization and M&A on the part of US conglomerates, but they aren't capturing compaies with ADRs or companies like Taro Pharmaceuticals (Israeli company with primary stock on the NYSE). If Novo Nordisk finds the cure for cancer or Germany spawns the next big AI player, that could tilt the value proposition quickly.
So I guess I'll continue to maintain my international exposure.