IMO, a rough but pretty good way to tell rigor in a subject at different schools is to look at how many undergrads they send in to PhD programs in a subject. If a school sends a lot of students in to PhD programs (absolute number or proportional) in a subject, that doesn’t mean they won’t have easy courses in that subject (some unis track) but it does mean that they definitely have the rigor, resources, and know-how to do well in PhD admissions and some kid can get a top education if they want it.
This holds even more for the top PhD programs in a subject.