Except student performance is falling across the world. What you said is the reason the US is like lower than most other western countries in outcomes. Its maybe less the reason that outcomes are getting worse across the board.

My gut says its just the reflection of a stratified global society. The billionaire and multimillionaire elites fund their schools very well while the rest struggle with collapsing budgets and parents that can't afford quality education. So countries with more cultural education values are weathering this crisis solely from extra public funding.

The way to validate this would be to see if recent drops in education correlate to funding.