I think it’s important to have access to graduate math classes but I don’t think the ranking of the grad school, esp USNWR, makes any difference. Even if the student takes grad classes as an UG, they will in all likelihood retake them in grad school unless they pass the comp exam in that particular area before they start the first year (unlikely to happen for most). Taking grad classes as an UG basically reassures the grad school admissions that you can handle those level classes, not that you have mastery over the material.
Re rankings: DS was recommended to attend one of the Group 1 schools for his PhD