I don't think many in the medical field would argue that Mayo Medical School provides a medical education that isn't top-of-the-line. It seems like a lot of questions on SDN about the school's "greatness" arise from the fact that it consistently ranks in the mid 20s instead of the top 10 on U.S News Rankings. From what I've heard, there are a couple reasons for the artificially lower ranking:
1) A lot of the great medicals schools that you point out (the top 10 U.S News schools, for example) are not just affiliated with strong hospital systems but are also university-affiliated (with some of the greatest undergraduate schools in the country). The resources/reputation that come from these affiliations are a part of the U.S News ranking formula. Since Mayo is not university-affiliated, it lacks those resources and thus has a lowered rank.
2) Mayo, on the whole, is more heavily focused on clinical research as opposed to basic science research, due to their huge emphasis on patient-centered medicine. The top ranked schools focus more extensively on basic science research, and thus have a higher amount of basic science grants/funding (especially from the NIH) compared to Mayo. This is a significant factor in the U.S News formula.
3) Related to number 2, Mayo funds a significant portion of its research using private donors and other non-federal sources. In 2014, only about $275 million of the $648 million Mayo Clinic research budget came from federal and state funding. The research-related factors that are part of the U.S News formula are based on NIH grants, so private research resources are not accounted for.
4) Student selection factors in the U.S News formula favor the top ranked schools. Mayo has a highly unique admissions process that is driven by their mission to train doctors that are patient, team, and service-oriented. Consequently, though it's acceptance rate (accepted/applied) is lower than any school in the top 20, the other objective statistics with greater weight in the U.S News formula tend to favor the top ranked schools (i.e. Mayo's average MCAT has been around 33/34 while Harvard/Hopkins etc. has been 36+)
Regardless of these factors, I think Mayo does't turn as many heads among premeds/the lay public compared to the U.S News top 10 because the long-standing history and appearance of U.S News have placed the company's rank list on an unnecessarily high pedestal. The best evidence for this is the fact that many other ranking websites and published lists have been around but aren't publicized/referenced as much. For example, StartClass lists UNC as #8 and Mayo as #13, while Duke and Columbia are #24 and #27 respectively. Likewise, the "What makes a top research medical school" paper that was recently published listed the University of Rochester as #12 and Mayo/Albert Einstein as #13, while UCSF was #17 and Michigan was #21. No one could credibly argue that Duke, Columbia, UCSF, or Michigan aren't great medical schools even if they aren't on the top of other lists. Accordingly, it doesn't make sense to consider medical schools outside the U.S News top 20 as any less great. Ultimately, all rankings suffer from biases introduced by the particular criteria the publisher chooses to emphasize---they should have minimal role in one's own evaluation of a school's greatness, relative to factors like personal fit, finances, and how the institution treats its student body.
