No single number is that meaningful on it’s own. But when a system has both lower standards and lower graduation rates that’s a clear sign of a problem.
Similarly, if your measuring graduates you need to ensure your measuring similar populations and one system is not simply dumping problems into a separate non counted category.
Doesn't the US have some sort of standard curriculum which defines what you have to do in order to graduate? Like you must have passing grades in at least N subjects.
I never understood the US focus on graduation rates when "graduation" can mean vastly different things depending on the school.