Flo isn't alleging infringement so the issue of copyrightability isn't in play, at least yet. But your suspicions about the copyrightability of rankings is well-founded because rankings and ratings do exist in a copyright grey zone.
The baseline requirement for all copyright worked is "originality," which theory rejects the mechanical arrangements of facts, such as a phone book. However, in Eckes v Card Prices Update, the second circuit recognized lists of baseball card prices as copyrightable as a compilation--the arrangement of facts based on the ranker's opinions contained sufficient originality. If a court can point to some minimal degree of creativity in the ranking process, it tends to meet the originality requirement. Ratings that merely arrangements of facts governed by some predetermined metric probably don't contain sufficient originality to qualify for copyright protection.
