Ranking departments is a pretty futile exercise, but subfield rankings are particularly stupid. The "theory", group in a department, for example, is often just a handful of people, and new hires, which happen all the time, totally change the makeup of the group. Also, the overall rankings change regularly. Go to archive.org to find old ones. For example: In this ranking, CMU is ranked #4 and Berkeley #1. Go back a few years, and its reversed. Go back more, and you can see it continue to fluctuate. You can also find Stanford and MIT out of the top spot. If the rankings were the same every year, no one would by magazines.